Led lighting systems and methods for constant current control in various operation modes

ABSTRACT

System and method for providing at least an output current to one or more light emitting diodes. The system includes a control component configured to receive at least a demagnetization signal, a sensed signal and a reference signal and to generate a control signal based on at least information associated with the demagnetization signal, the sensed signal and the reference signal, and a logic and driving component configured to receive at least the control signal and output a drive signal to a switch based on at least information associated with the control signal. The switch is connected to a first diode terminal of a diode and a first inductor terminal of an inductor. The diode further includes a second diode terminal, and the inductor further includes a second inductor terminal.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201110376439.0, filed Nov. 15, 2011, incorporated by reference hereinfor all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides lighting systems and methods forconstant current control in various operation modes. Merely by way ofexample, the invention has been applied to one or more light emittingdiodes. But it would be recognized that the invention has a much broaderrange of applicability.

Generally, a conventional lighting system for light emitting diodes(LEDs) often uses a floating Buck converter. This type of LED lightingsystem usually is cost effective with compact size. FIG. 1 is asimplified diagram showing a conventional LED lighting system with aBuck converter. The lighting system 100 includes apulse-width-modulation (PWM) controller 110, a power switch 120, a diode130, an inductor 140, capacitors 150 and 152, and a sensing resistor160. Additionally, the lighting system 100 receives an input voltage andprovides a lamp current and a lamp voltage to one or more LEDs 190.

As shown in FIG. 1, the power switch 120 includes terminals 122, 124,and 126. The PWM controller 110 outputs a drive signal 112 and receivesa current sensing signal 114. The drive signal 112 corresponds to aswitching period (e.g., T_(s)). For example, the power switch 120 is aMOS transistor. In another example, the power switch 120 is a bipolartransistor (e.g. an NPN bipolar transistor). In yet another example, thepower switch 120 is an insulated gate bipolar transistor (IGBT).

It is highly desirable to improve the techniques of constant currentcontrol, so that a constant lamp current can be achieved in the DCMmode, the CCM mode and the critical conduction mode (CRM), and both highpower factor and precision control can be realized.

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides lighting systems and methods forconstant current control in various operation modes. Merely by way ofexample, the invention has been applied to one or more light emittingdiodes. But it would be recognized that the invention has a much broaderrange of applicability.

According to another embodiment, a system for providing at least anoutput current to one or more light emitting diodes includes a controlcomponent configured to receive at least a demagnetization signal, asensed signal and a reference signal and to generate a control signalbased on at least information associated with the demagnetizationsignal, the sensed signal and the reference signal, and a logic anddriving component configured to receive at least the control signal andoutput a drive signal to a switch based on at least informationassociated with the control signal. The switch is connected to a firstdiode terminal of a diode and a first inductor terminal of an inductor.The diode further includes a second diode terminal, and the inductorfurther includes a second inductor terminal. The second diode terminaland the second inductor terminal are configured to provide at least theoutput current to the one or more light emitting diodes. The controlsignal is configured to regulate the output current at a constantmagnitude.

According to yet another embodiment, a method for providing at least anoutput current to one or more light emitting diodes includes receivingat least a demagnetization signal, a sensed signal and a referencesignal, processing information associated with the demagnetizationsignal, the sensed signal and the reference signal, and generating acontrol signal based on at least information associated with thedemagnetization signal, the sensed signal and the reference signal.Additionally, the method includes receiving at least the control signal,processing information associated with the control signal, andoutputting a drive signal to a switch connected to a first diodeterminal of a diode and a first inductor terminal of an inductor. Thediode further includes a second diode terminal, and the inductor furtherincludes a second inductor terminal. The second diode terminal and thesecond inductor terminal are configured to provide at least the outputcurrent to the one or more light emitting diodes. Moreover, the methodincludes regulating the output current at a predetermined magnitudebased on at least information associated with the control signal.

According to yet another embodiment, a system for providing at least anoutput current to one or more light emitting diodes includes a firstsignal processing component configured to receive at least a sensedsignal and generate a first signal. The sensed signal is associated withan inductor current flowing through an inductor coupled to a switch.Additionally, the system includes a second signal processing componentconfigured to generate a second signal, an integrator componentconfigured to receive the first signal and the second signal andgenerate a third signal, and a comparator configured to processinformation associated with the third signal and the sensed signal andgenerate a comparison signal based on at least information associatedwith the third signal and the sensed signal. Moreover, the systemincludes a signal generator configured to receive at least thecomparison signal and generate a modulation signal, and a gate driverconfigured to receive the modulation signal and output a drive signal tothe switch. The drive signal is associated with at least one or moreswitching periods, and each of the one or more switching periodsincludes at least an on-time period for the switch and a demagnetizationperiod for a demagnetization process. For each of the one or moreswitching periods, the first signal represents a multiplication resultof a first sum of the on-time period and the demagnetization period anda second sum of a first current magnitude and a second currentmagnitude, and the second signal represents the switching periodmultiplied by a predetermined current magnitude. The first currentmagnitude represents the inductor current at the beginning of theon-time period, and the second current magnitude represents the inductorcurrent at the end of the on-time period. The integrator component isfurther configured to integrate period-by-period differences between thefirst signal and the second signal for a plurality of switching periods,and the third signal represents the integrated period-by-perioddifferences. The integrated period-by-period differences are smallerthan a predetermined threshold in magnitude.

According to yet another embodiment, a method for providing at least anoutput current to one or more light emitting diodes includes receivingat least a sensed signal. The sensed signal is associated with aninductor current flowing through an inductor coupled to a switch.Additionally, the method includes processing information associated withthe sensed signal, generating a first signal based on at leastinformation associated with the sensed signal, generating a secondsignal, receiving the first signal and the second signal, processinginformation associated with the first signal and the second signal, andgenerating a third signal based on at least information associated withthe first signal and the second signal. Moreover, the method includesprocessing information associated with the third signal and the sensedsignal, generating a comparison signal based on at least informationassociated with the third signal and the sensed signal, receiving atleast the comparison signal, generating a modulation signal based on atleast information associated with the comparison signal, receiving themodulation signal, and outputting a drive signal based on at leastinformation associated with the modulation signal. The drive signal isassociated with at least one or more switching periods, and each of theone or more switching periods includes at least an on-time period and ademagnetization period. For each of the one or more switching periods,the first signal represents a multiplication result of a first sum ofthe on-time period and the demagnetization period and a second sum of afirst current magnitude and a second current magnitude, and the secondsignal represents the switching period multiplied by a predeterminedcurrent magnitude. The first current magnitude represents the inductorcurrent at the beginning of the on-time period, and the second currentmagnitude represents the inductor current at the end of the on-timeperiod. The process for processing information associated with the firstsignal and the second signal includes integrating period-by-perioddifferences between the first signal and the second signal for aplurality of switching periods, and the third signal represents theintegrated period-by-period differences. The integrated period-by-perioddifferences are smaller than a predetermined threshold in magnitude.

According to yet another embodiment, a system for providing at least anoutput current to one or more light emitting diodes includes a firstsignal processing component configured to receive at least a sensedsignal and generate a first signal. The sensed signal is associated withan inductor current flowing through an inductor coupled to a switch.Additionally, the system includes a second signal processing componentconfigured to generate a second signal, an integrator componentconfigured to receive the first signal and the second signal andgenerate a third signal, and a comparator configured to processinformation associated with the third signal and the sensed signal andgenerate a comparison signal based on at least information associatedwith the third signal and the sensed signal. Moreover, the systemincludes a signal generator configured to receive at least thecomparison signal and generate a modulation signal, and a gate driverconfigured to receive the modulation signal and output a drive signal tothe switch. The drive signal is associated with at least one or moreswitching periods, and each of the one or more switching periodsincludes at least an on-time period for the switch and a demagnetizationperiod for a demagnetization process. For each of the one or moreswitching periods, the first signal represents a sum of a firstmultiplication result and a second multiplication result, and the secondsignal represents the switching period multiplied by a predeterminedcurrent magnitude. The first multiplication result is equal to theon-time period multiplied by a sum of a first current magnitude and asecond current magnitude. The first current magnitude represents theinductor current at the beginning of the on-time period, and the secondcurrent magnitude represents the inductor current at the end of theon-time period. The second multiplication result is equal to twomultiplied by the demagnetization period and further multiplied by athird current magnitude, and the third current magnitude represents theinductor current at the middle of the on-time period. The integratorcomponent is further configured to integrate period-by-perioddifferences between the first signal and the second signal for aplurality of switching periods, and the third signal represents theintegrated period-by-period differences. The integrated period-by-perioddifferences are smaller than a predetermined threshold in magnitude.

According to yet another embodiment, a method for providing at least anoutput current to one or more light emitting diodes includes receivingat least a sensed signal. The sensed signal is associated with aninductor current flowing through an inductor coupled to a switch.Additionally, the method includes processing information associated withthe sensed signal, generating a first signal based on at leastinformation associated with the sensed signal, generating a secondsignal, receiving the first signal and the second signal, processinginformation associated with the first signal and the second signal, andgenerating a third signal based on at least information associated withthe first signal and the second signal. Moreover, the method includesprocessing information associated with the third signal and the sensedsignal, generating a comparison signal based on at least informationassociated with the third signal and the sensed signal, receiving atleast the comparison signal, and generating a modulation signal based onat least information associated with the comparison signal. Also, themethod includes receiving the modulation signal, and outputting a drivesignal based on at least information associated with the modulationsignal. The drive signal is associated with at least one or moreswitching periods, and each of the one or more switching periodsincludes at least an on-time period and a demagnetization period. Foreach of the one or more switching periods, the first signal represents asum of a first multiplication result and a second multiplication result,and the second signal represents the switching period multiplied by apredetermined current magnitude. The first multiplication result isequal to the on-time period multiplied by a sum of a first currentmagnitude and a second current magnitude. The first current magnituderepresents the inductor current at the beginning of the on-time period,and the second current magnitude represents the inductor current at theend of the on-time period. The second multiplication result is equal totwo multiplied by the demagnetization period and further multiplied by athird current magnitude, and the third current magnitude represents theinductor current at the middle of the on-time period. The process forprocessing information associated with the first signal and the secondsignal includes integrating period-by-period differences between thefirst signal and the second signal for a plurality of switching periods,and the third signal represents the integrated period-by-perioddifferences. The integrated period-by-period differences are smallerthan a predetermined threshold in magnitude.

According to yet another embodiment, a system for providing at least anoutput current to one or more light emitting diodes includes a firstsampling-and-holding and voltage-to-current-conversion componentconfigured to receive at least a sensed signal and generate a firstcurrent signal. The sensed signal is associated with an inductor currentflowing through an inductor coupled to a first switch. Additionally, thesystem includes a second sampling-and-holding andvoltage-to-current-conversion component configured to receive at leastthe sensed signal and generate a second current signal, and asignal-amplification and voltage-to-current-conversion componentconfigured to receive at least the sensed signal and generate a thirdcurrent signal. Moreover, the system includes a current-signal generatorconfigured to generate a fourth current signal, and a capacitor coupledto the current-signal generator, coupled through a second switch to thefirst sampling-and-holding and voltage-to-current-conversion componentand the second sampling-and-holding and voltage-to-current-conversioncomponent, and coupled through a third switch to thesignal-amplification and voltage-to-current-conversion component. Thecapacitor is configured to generate a voltage signal. Also, the systemincludes a comparator configured to process information associated withthe voltage signal and the sensed signal and generate a comparisonsignal based on at least information associated with the voltage signaland the sensed signal. Additionally, the system includes amodulation-signal generator configured to receive at least thecomparison signal and generate a modulation signal, and a gate driverconfigured to receive the modulation signal and output a drive signal tothe first switch. The drive signal is associated with at least one ormore switching periods, and each of the one or more switching periodsincludes at least an on-time period for the first switch and ademagnetization period for a demagnetization process. The first currentsignal represents the inductor current at the beginning of the on-timeperiod, the second current signal represents the inductor current at theend of the on-time period, and the third current signal represents theinductor current. For each of the one or more switching periods, thefirst current signal and the second current signal are configured todischarge or charge the capacitor during only the demagnetizationperiod, the third current signal is configured to discharge or chargethe capacitor during only the on-time period, and the fourth currentsignal is configured to charge or discharge the capacitor during theswitching period.

According to yet another embodiment, a method for providing at least anoutput current to one or more light emitting diodes includes receivingat least a sensed signal. The sensed signal is associated with aninductor current flowing through an inductor coupled to a switch,processing information associated with the sensed signal, and generatinga first current signal, a second current signal, and a third currentsignal based on at least information associated with the sensed signal.Additionally, the method includes generating a fourth current signal,processing information associated with the first current signal, thesecond current signal, the third current signal, and the fourth currentsignal, and generating a voltage signal, by at least a capacitor, basedon at least information associated with the first current signal, thesecond current signal, the third current signal, and the fourth currentsignal. Moreover, the method includes processing information associatedwith the voltage signal and the sensed signal, generating a comparisonsignal based on at least information associated with the voltage signaland the sensed signal, receiving at least the comparison signal, andgenerating a modulation signal based on at least information associatedwith the comparison signal. Also, the method includes receiving themodulation signal, and outputting a drive signal based on at leastinformation associated with the modulation signal. The drive signal isassociated with at least one or more switching periods, and each of theone or more switching periods includes at least an on-time period and ademagnetization period. The first current signal represents the inductorcurrent at the beginning of the on-time period, the second currentsignal represents the inductor current at the end of the on-time period,and the third current signal represents the inductor current. For eachof the one or more switching periods, the process for processinginformation associated with the first current signal, the second currentsignal, the third current signal, and the fourth current signal includesdischarging or charging the capacitor with the first current signal andthe second current signal during only the demagnetization period,discharging or charging the capacitor with the third current signalduring only the on-time period, and charging or discharging thecapacitor with the fourth current signal during the switching period.

According to yet another embodiment, a system for providing at least anoutput current to one or more light emitting diodes includes asignal-amplification and voltage-to-current-conversion componentconfigured to receive at least a sensed signal and generate a firstcurrent signal. The sensed signal is associated with an inductor currentflowing through an inductor coupled to a first switch. Additionally, thesystem includes a current-signal generator configured to generate asecond current signal, and a capacitor coupled to the current-signalgenerator, and coupled through a second switch to thesignal-amplification and voltage-to-current-conversion component. Thecapacitor is configured to generate a voltage signal. Moreover, thesystem includes a comparator configured to process informationassociated with the voltage signal and the sensed signal and generate acomparison signal based on at least information associated with thevoltage signal and the sensed signal, a modulation-signal generatorconfigured to receive at least the comparison signal and generate amodulation signal, and a gate driver configured to receive themodulation signal and output a drive signal to the first switch. Thedrive signal is associated with at least one or more switching periods,and the first current signal represents the inductor current. Each ofthe one or more switching periods includes at least an on-time periodfor the first switch. For each of the one or more switching periods, thefirst current signal is configured to discharge or charge the capacitorduring only the on-time period, and the second current signal isconfigured to charge or discharge the capacitor during only the on-timeperiod.

According to yet another embodiment, a method for providing at least anoutput current to one or more light emitting diodes includes receivingat least a sensed signal. The sensed signal is associated with aninductor current flowing through an inductor coupled to a switch.Additionally, the method includes processing information associated withthe sensed signal, generating a first current signal based on at leastinformation associated with the sensed signal, generating a secondcurrent signal, processing information associated with the first currentsignal and the second current signal, and generating a voltage signal,by at least a capacitor, based on at least information associated withthe first current signal and the second current signal. Moreover, themethod includes processing information associated with the voltagesignal and the sensed signal, generating a comparison signal based on atleast information associated with the voltage signal and the sensedsignal, receiving at least the comparison signal, generating amodulation signal based on at least information associated with thecomparison signal, receiving the modulation signal, and outputting adrive signal based on at least information associated with themodulation signal. The drive signal is associated with at least one ormore switching periods, and the first current signal represents theinductor current. Each of the one or more switching periods includes atleast an on-time period. For each of the one or more switching periods,the process for processing information associated with the first currentsignal and the second current signal includes discharging or chargingthe capacitor with the first current signal during only the on-timeperiod, and charging or discharging the capacitor with the secondcurrent signal during only the on-time period.

According to yet another embodiment, a system for providing at least anoutput current to one or more light emitting diodes includes atransconductance amplifier configured to receive a sensed signal andalso receive a predetermined voltage signal through a first switch. Thesensed signal is associated with an inductor current flowing through aninductor coupled to a second switch, and the transconductance amplifieris further configured to generate a current signal. Additionally, thesystem includes a capacitor coupled to the transconductance amplifierand configured to generate a voltage signal, and a comparator configuredto process information associated with the voltage signal and the sensedsignal and generate a comparison signal based on at least informationassociated with the voltage signal and the sensed signal. Moreover, thesystem includes a modulation-signal generator configured to receive atleast the comparison signal and generate a modulation signal, and a gatedriver configured to receive the modulation signal and output a drivesignal to the second switch. The drive signal is associated with atleast one or more switching periods, and each of the one or moreswitching periods includes at least an on-time period for the secondswitch. The transconductance amplifier is further configured to, foreach of the one or more switching periods, receive at least apredetermined voltage signal only during the on-time period. The currentsignal is configured to charge or discharge the capacitor.

According to yet another embodiment, a method for providing at least anoutput current to one or more light emitting diodes includes receivingat least a sensed signal. The sensed signal is associated with aninductor current flowing through an inductor coupled to a switch.Additionally, the method includes processing information associated withthe sensed signal and a predetermined voltage signal, generating acurrent signal based on at least information associated with the sensedsignal and the predetermined voltage signal, and processing informationassociated with the current signal. Moreover, the method includesgenerating a voltage signal, by at least a capacitor, based on at leastinformation associated with the current signal, processing informationassociated with the voltage signal and the sensed signal, and generatinga comparison signal based on at least information associated with thevoltage signal and the sensed signal. Also, the method includesreceiving at least the comparison signal, generating a modulation signalbased on at least information associated with the comparison signal,receiving the modulation signal, and outputting a drive signal based onat least information associated with the modulation signal. The drivesignal is associated with at least one or more switching periods, andeach of the one or more switching periods includes at least an on-timeperiod. The process for receiving at least a sensed signal includes, foreach of the one or more switching periods, receiving at least thepredetermined voltage signal during only the on-time period. Also, theprocess for processing information associated with the current signalincludes charging or discharging the capacitor with the current signal.

According to yet another embodiment, a system for providing at least anoutput current to one or more light emitting diodes includes a firstsampling-and-holding and voltage-to-current-conversion componentconfigured to receive at least a sensed signal and generate a firstcurrent signal. The sensed signal is associated with an inductor currentflowing through an inductor coupled to a first switch. Additionally, thesystem includes a second sampling-and-holding andvoltage-to-current-conversion component configured to receive at leastthe sensed signal and generate a second current signal, and asignal-amplification and voltage-to-current-conversion componentconfigured to receive at least the sensed signal and generate a thirdcurrent signal, a current-signal generator configured to generate afourth current signal, and a capacitor coupled to the current-signalgenerator, coupled through a second switch to the firstsampling-and-holding and voltage-to-current-conversion component and thesecond sampling-and-holding and voltage-to-current-conversion component,and coupled through a third switch to the signal-amplification andvoltage-to-current-conversion component, the capacitor being configuredto generate a first voltage signal. Moreover, the system includes amultiplier component configured to process information associated withthe first voltage signal and a second voltage signal and generate amultiplication signal based on at least information associated with thefirst voltage signal and the second voltage signal. Also, the systemincludes a comparator configured to receive the multiplication signaland the sensed signal and generate a comparison signal based on at leastinformation associated with the multiplication signal and the sensedsignal, a modulation-signal generator configured to receive at least thecomparison signal and generate a modulation signal, and a gate driverconfigured to receive the modulation signal and output a drive signal tothe first switch. The drive signal is associated with at least aplurality of switching periods, and each of the one or more switchingperiods includes at least an on-time period for the first switch and ademagnetization period for a demagnetization process. The first currentsignal represents the inductor current at the beginning of the on-timeperiod, the second current signal represents the inductor current at theend of the on-time period, and the third current signal represents theinductor current. For the plurality of switching periods, the firstcurrent signal and the second current signal are configured to dischargeor charge the capacitor during only the demagnetization period, thethird current signal is configured to discharge or charge the capacitorduring only the on-time period, and the fourth current signal isconfigured to charge or discharge the capacitor during the switchingperiod.

According to yet another embodiment, a method for providing at least anoutput current to one or more light emitting diodes includes receivingat least a sensed signal. The sensed signal is associated with aninductor current flowing through an inductor coupled to a switch.Additionally, the method includes processing information associated withthe sensed signal, and generating a first current signal, a secondcurrent signal, and a third current signal based on at least informationassociated with the sensed signal. Moreover, the method includesgenerating a fourth current signal, processing information associatedwith the first current signal, the second current signal, the thirdcurrent signal, and the fourth current signal, and generating a firstvoltage signal, by at least a capacitor, based on at least informationassociated with the first current signal, the second current signal, thethird current signal, and the fourth current signal. Also, the methodincludes processing information associated with the first voltage signaland a second voltage signal, generating a multiplication signal based onat least information associated with the first voltage signal and thesecond voltage signal, receiving the multiplication signal and thesensed signal, and generating a comparison signal based on at leastinformation associated with the multiplication signal and the sensedsignal. Additionally, the method includes receiving at least thecomparison signal, generating a modulation signal based on at leastinformation associated with the comparison signal, receiving themodulation signal, and outputting a drive signal based on at leastinformation associated with the modulation signal. The drive signal isassociated with at least a plurality of switching periods, and each ofthe plurality of switching periods includes at least an on-time periodand a demagnetization period. The first current signal represents theinductor current at the beginning of the on-time period, the secondcurrent signal represents the inductor current at the end of the on-timeperiod, and the third current signal represents the inductor current.For each of the plurality of switching periods, the process forprocessing information associated with the first current signal, thesecond current signal, the third current signal, and the fourth currentsignal includes discharging or charging the capacitor with the firstcurrent signal and the second current signal during only thedemagnetization period, discharging or charging the capacitor with thethird current signal during only the on-time period, and charging ordischarging the capacitor with the fourth current signal during theswitching period.

According to yet another embodiment, a system for providing at least anoutput current to one or more light emitting diodes includes atransconductance amplifier configured to receive a sensed signal andalso receive a predetermined voltage signal through a first switch. Thesensed signal is associated with an inductor current flowing through aninductor coupled to a second switch, and the transconductance amplifieris further configured to generate a current signal. Additionally, thesystem includes a capacitor coupled to the transconductance amplifierand configured to generate a voltage signal, and a comparator configuredto process information associated with the voltage signal and a rampingsignal and generate a comparison signal based on at least informationassociated with the voltage signal and the ramping signal. Moreover, thesystem includes a modulation-signal generator configured to receive atleast the comparison signal and generate a modulation signal, and a gatedriver configured to receive the modulation signal and output a drivesignal to the second switch. The drive signal is associated with atleast one or more switching periods, each of the one or more switchingperiods including at least an on-time period for the second switch. Thetransconductance amplifier is further configured to, for each of the oneor more switching periods, receive at least a predetermined voltagesignal only during the on-time period. The current signal is configuredto charge or discharge the capacitor.

According to yet another embodiment, a method for providing at least anoutput current to one or more light emitting diodes includes receivingat least a sensed signal. The sensed signal is associated with aninductor current flowing through an inductor coupled to a switch.Additionally, the method includes processing information associated withthe sensed signal and a predetermined voltage signal, generating acurrent signal based on at least information associated with the sensedsignal and the predetermined voltage signal, processing informationassociated with the current signal, and generating a voltage signal, byat least a capacitor, based on at least information associated with thecurrent signal. Moreover, the method includes processing informationassociated with the voltage signal and a ramping signal, generating acomparison signal based on at least information associated with thevoltage signal and the ramping signal, receiving at least the comparisonsignal, and generating a modulation signal based on at least informationassociated with the comparison signal. Also, the method includesreceiving the modulation signal and outputting a drive signal based onat least information associated with the modulation signal. The drivesignal is associated with at least one or more switching periods, andeach of the one or more switching periods includes at least an on-timeperiod. The process for receiving at least a sensed signal includes, foreach of the one or more switching periods, receiving at least apredetermined voltage signal only during the on-time period, and theprocess for processing information associated with the current signalincludes charging or discharging the capacitor with the current signal.

According to yet another embodiment, a system for providing at least anoutput current to one or more light emitting diodes includes atransconductance amplifier configured to receive a sensed signal andalso receive a predetermined voltage signal through a first switch. Thesensed signal is associated with an inductor current flowing through aninductor coupled to a second switch, and the transconductance amplifieris further configured to generate a current signal. Additionally, thesystem includes a capacitor coupled to the transconductance amplifierand configured to generate a first voltage signal, and a multipliercomponent configured to process information associated with the firstvoltage signal and a second voltage signal and generate a multiplicationsignal based on at least information associated with the first voltagesignal and the second voltage signal. Moreover, the system includes acomparator configured to receive the multiplication signal and thesensed signal and generate a comparison signal based on at leastinformation associated with the multiplication signal and the sensedsignal, a modulation-signal generator configured to receive at least thecomparison signal and generate a modulation signal, and a gate driverconfigured to receive the modulation signal and output a drive signal tothe second switch. The drive signal is associated with at least one ormore switching periods, each of the one or more switching periodsincluding at least an on-time period for the second switch. Thetransconductance amplifier is further configured to, for each of the oneor more switching periods, receive at least a predetermined voltagesignal during only the on-time period. The current signal is configuredto charge or discharge the capacitor.

According to yet another embodiment, a method for providing at least anoutput current to one or more light emitting diodes includes receivingat least a sensed signal. The sensed signal is associated with aninductor current flowing through an inductor coupled to a switch.Additionally, the method includes processing information associated withthe sensed signal and a predetermined voltage signal, generating acurrent signal based on at least information associated with the sensedsignal and the predetermined voltage signal, processing informationassociated with the current signal, and generating a first voltagesignal, by at least a capacitor, based on at least informationassociated with the current signal. Moreover, the method includesprocessing information associated with the first voltage signal and asecond voltage signal, generating a multiplication signal based on atleast information associated with the first voltage signal and thesecond voltage signal, receiving the multiplication signal and thesensed signal, and generating a comparison signal based on at leastinformation associated with the multiplication signal and the sensedsignal. Also, the method includes receiving at least the comparisonsignal, generating a modulation signal based on at least informationassociated with the comparison signal, receiving the modulation signal,and outputting a drive signal based on at least information associatedwith the modulation signal. The drive signal is associated with at leastone or more switching periods, and each of the one or more switchingperiods includes at least an on-time period. The process for receivingat least a sensed signal includes, for each of the one or more switchingperiods, receiving at least a predetermined voltage signal during onlythe on-time period, and the process for processing informationassociated with the current signal includes charging or discharging thecapacitor with the current signal.

According to yet another embodiment, a system for providing at least anoutput current to one or more light emitting diodes includes a firstsignal processing component configured to receive at least a sensedsignal and generate a first signal. The sensed signal is associated withan inductor current flowing through an inductor coupled to a switch.Additionally, the system includes a second signal processing componentconfigured to generate a second signal, an integrator componentconfigured to receive the first signal and the second signal andgenerate a third signal, a comparator configured to process informationassociated with the third signal and the sensed signal and generate acomparison signal based on at least information associated with thethird signal and the sensed signal. Moreover, the system includes asignal generator configured to receive at least the comparison signaland generate a modulation signal, and a gate driver configured toreceive the modulation signal and output a drive signal to the switch.The drive signal is associated with at least one or more switchingperiods, and each of the one or more switching periods includes at leastan on-time period for the switch and a demagnetization period for ademagnetization process. The first signal processing component isfurther configured to, for each of the one or more switching periods,sample the sensed signal at the middle of the on-time period, hold thesampled sensed signal representing the inductor current at the middle ofthe on-time period, and generate the first signal representing a sum ofa first multiplication result and a second multiplication result basedon at least information associated with the held and sampled sensedsignal. For each of the one or more switching periods, the second signalrepresents the switching period multiplied by a predetermined currentmagnitude. The integrator component is further configured to integrateperiod-by-period differences between the first signal and the secondsignal for a plurality of switching periods, and the third signalrepresents the integrated period-by-period differences. The integratedperiod-by-period differences are smaller than a predetermined thresholdin magnitude.

According to yet another embodiment, a method for providing at least anoutput current to one or more light emitting diodes includes receivingat least a sensed signal. The sensed signal is associated with aninductor current flowing through an inductor coupled to a switch.Additionally, the method includes processing information associated withthe sensed signal, generating a first signal based on at leastinformation associated with the sensed signal, generating a secondsignal, receiving the first signal and the second signal, processinginformation associated with the first signal and the second signal, andgenerating a third signal based on at least information associated withthe first signal and the second signal. Moreover, the method includesprocessing information associated with the third signal and the sensedsignal, generating a comparison signal based on at least informationassociated with the third signal and the sensed signal, receiving atleast the comparison signal, and generating a modulation signal based onat least information associated with the comparison signal. Also, themethod includes receiving the modulation signal, and outputting a drivesignal based on at least information associated with the modulationsignal. The drive signal is associated with at least one or moreswitching periods, and each of the one or more switching periodsincludes at least an on-time period for the switch and a demagnetizationperiod for a demagnetization process. The process for processinginformation associated with the sensed signal includes, for each of theone or more switching periods, sampling the sensed signal at the middleof the on-time period, and holding the sampled sensed signalrepresenting the inductor current at the middle of the on-time period.For each of the one or more switching periods, the first signalrepresents a sum of a first multiplication result and a secondmultiplication result generated based on at least information associatedwith the held and sampled sensed signal, and the second signalrepresents the switching period multiplied by a predetermined currentmagnitude. The process for processing information associated with thefirst signal and the second signal includes integrating period-by-perioddifferences between the first signal and the second signal for aplurality of switching periods, and the third signal represents theintegrated period-by-period differences. The integrated period-by-perioddifferences are smaller than a predetermined threshold in magnitude.

Depending upon embodiment, one or more benefits may be achieved. Thesebenefits and various additional objects, features and advantages of thepresent invention can be fully appreciated with reference to thedetailed description and accompanying drawings that follow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram showing a conventional LED lightingsystem with a Buck converter.

FIG. 2 is a simplified diagram showing an operation mechanism for thelighting system that operates in the discontinuous conduction mode(DCM).

FIG. 3 is a simplified diagram showing an LED lighting system accordingto one embodiment of the present invention.

FIGS. 4(A), (B), and (C) are simplified diagrams showing timing diagramsfor the lighting system 300 that operates in the discontinuousconduction mode (DCM), the continuous conduction mode (CCM), and thecritical conduction mode (CRM), respectively.

FIG. 5 is a simplified diagram for a LED lighting system according toanother embodiment of the present invention.

FIG. 6 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention.

FIG. 7 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention.

FIG. 8 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention.

FIG. 9 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention.

FIG. 10 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention.

FIG. 11 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention.

FIG. 12 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides lighting systems and methods forconstant current control in various operation modes. Merely by way ofexample, the invention has been applied to one or more light emittingdiodes. But it would be recognized that the invention has a much broaderrange of applicability.

FIG. 2 is a simplified diagram showing an operation mechanism for thelighting system 100 that operates in the discontinuous conduction mode(DCM). The waveform 210 represents a voltage between the terminals 122and 124 (e.g., V_(DS)) as a function of time, the waveform 220represents a current flowing through the inductor 140 (e.g. I_(L)) as afunction of time, and the waveform 230 represents the current sensingsignal 114 (e.g., V_(CS)) as a function of time.

For example, when the power switch 120 is turned on (e.g., duringT_(on)), the inductor 140 is magnetized and the current that flowsthrough the inductor 140 (e.g. I_(L)) flows through the power switch 120and the sensing resistor 160. The sensing resistor 160 converts theinductor current (e.g. I_(L)) into the current sensing signal 114 (e.g.,V_(CS)). In another example, when the power switch 120 is turned off(e.g., during T_(off)), the inductor 140 is demagnetized and theinductor current (e.g. I_(L)) flows through the diode 130, the capacitor150, and the one or more LEDs 190. In yet another example, a lampcurrent 192 (e.g., an output current) that flows through the one or moreLEDs 190 (e.g., I_(LED)) is equal to the average of the inductor current(e.g., the average of I_(L)). If the average of the inductor current isregulated to a predetermined level, the lamp current 192 is alsoregulated to the predetermined level. Therefore, the lamp current 192can be estimated by sensing the inductor current (e.g. I_(L)) throughthe sensing resistor 160 and calculating the on-time of the power switch120 (e.g., T_(on)).

As discussed above, the lighting system 100 attempts to control the lampcurrent 192 by controlling the peak magnitude of the inductor current(e.g. I_(L)). The lamp current 192 is equal to the average of theinductor current, but the relationship between the average of theinductor current and the peak magnitude of the inductor current dependson the input AC voltage (e.g., VAC). For example, if the conventionallighting system 100 operates, with a fixed switching frequency, in thecontinuous conduction mode (CCM) or the discontinuous conduction mode(DCM), the on-time should decrease with increasing input AC voltage(e.g., VAC) in order to control the peak magnitude of the inductorcurrent. As a result, the average of the inductor current and the lampcurrent 192 also decrease with increasing input AC voltage. Therefore,the lamp current 192 does not remain constant with respect to variousinput AC voltages.

FIG. 3 is a simplified diagram showing an LED lighting system accordingto one embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. The lighting system 300 includes apulse-width-modulation (PWM) controller 310, a switch 320, a diode 330,an inductor 340, capacitors 350 and 352, a sensing resistor 360, and acapacitor 364.

For example, the switch 320, the diode 330, the inductor 340, thecapacitor 350, and the sensing resistor 360 are the same as the powerswitch 120, the diode 130, the inductor 140, the capacitor 150, and thesensing resistor 160, respectively. In another example, the switch 320is a MOS transistor. In yet another example, the switch 320 is a bipolartransistor (e.g. an NPN bipolar transistor). In yet another example, theswitch 320 is an insulated gate bipolar transistor (IGBT).

In one embodiment, the PWM controller 310 includes a constant-currentcontrol component 380, a demagnetization component 382, anover-current-protection (OCP) component 384, a clock generator 386, areference signal generator 388, a logic component 362, a flip-flopcomponent 394, a drive component 396, and a leading-edge-blankingcomponent 308. In another embodiment, the PWM controller includesterminals 372, 374, 376, 378, and 379.

As shown in FIG. 3, the lighting system 300 receives an input voltage332 and provides a lamp current 392 (e.g., an output current) and a lampvoltage to one or more LEDs 390. For example, the PWM controller 310outputs a drive signal 312 through the terminal 372 to the switch 320.In another example, the drive signal 312 corresponds to a switchingperiod (e.g., T_(s)). According to one embodiment, if the switch 320 isturned on (e.g., during T_(on)), the current that flows through theinductor 340 (e.g. I_(L)) is sensed by the sensing resistor 360, andconsequently, a current sensing signal 314 (e.g., V_(cs)) is received bythe over-current-protection (OCP) component 384 through the terminal 374and the leading-edge-blanking component 308. For example, in response,the over-current-protection (OCP) component 384 generates a controlsignal 385.

According to another embodiment, the demagnetization component 382receives a signal 354 through the terminal 376 from the capacitor 352,and in response generates a demagnetization signal 383. According to yetanother embodiment, the clock generator 386 generates a clock signal387, and the reference signal generator 388 generates a referencevoltage signal 381 (e.g., V_(REF)) and a reference current signal 389(e.g., I_(REF)).

In one embodiment, the drive signal 312, the current sensing signal 314,the demagnetization signal 383, the clock signal 387, and the referencecurrent signal 389 are received by the constant-current controlcomponent 380 connected to the capacitor 364 (e.g., through the terminal378). For example, in response, the constant-current control component380 outputs a control signal 391 to the logic component 362. In anotherexample, the logic component 362 receives the control signals 391 and385 and outputs a logic signal 393. In another embodiment, the logicsignal 393 is received by the flip-flop component 394, which alsoreceives the clock signal 387 and generates a modulation signal 395. Forexample, the modulation signal 395 is received by the drive component396. In another example, the drive component 396 generate the drivesignal 312 based on at least the modulation signal 395.

The lighting system 300 can regulate the lamp current 392 that flowsthrough the one or more LEDs 390 (e.g., I_(LED)) in various operationmodes, such as the discontinuous conduction mode (DCM), the continuousconduction mode (CCM), and/or the critical conduction mode (CRM),according to certain embodiments. For example, the lamp current 392 ismaintained at a constant level, regardless of the lamp voltage, theinductance of the inductor 340, and/or the input voltage 332.

FIGS. 4(A), (B), and (C) are simplified diagrams showing timing diagramsfor the lighting system 300 that operates in the discontinuousconduction mode (DCM), the continuous conduction mode (CCM), and thecritical conduction mode (CRM), respectively.

As shown in FIG. 4(A), in DCM, the off-time of the switch 320, T_(off),is much longer than the demagnetization period, T_(demag). Thedemagnetization process ends at point C, and the next switching cyclestarts after the completion of the demagnetization process. Thedemagnetization period is determined as follows:

$\begin{matrix}{T_{demag} = {\frac{I_{L\; \_ \; p}}{\left( {V_{o}/L} \right)} = \frac{I_{L\; \_ \; p} \times L}{V_{o}}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

where V_(o) represents the lamp voltage across the one or more LEDs 390,I_(L) _(_) _(p) represents the peak magnitude of the inductor current(e.g., I_(L)) at the end of the on-time of the switch 320. Additionally,L represents the inductance of the inductor 340. Moreover, as shown inFIG. 4(A), I_(L) _(_) ₀ represents the initial magnitude of the inductorcurrent (e.g., I_(L)) at the beginning of the on-time of the switch 320,and is equal to zero.

In DCM, the lamp current 392, which is equal to the average inductorcurrent, is as follows:

$\begin{matrix}{I_{out} = {\frac{1}{2} \times I_{L\; \_ \; p} \times \frac{T_{demag} + T_{on}}{T_{s}}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

where I_(out) represents the lamp current 392, and T_(on) represents theon-time of the switch 320.

As shown in FIG. 4(B), in CCM, the next switching cycle starts beforethe demagnetization process is completed. The off-time of the switch320, T_(off), is shorter than the demagnetization period, T_(demag). InCCM, the lamp current 392, which is equal to the average inductorcurrent, is determined as follows:

$\begin{matrix}{I_{out} = {{\frac{1}{2} \times \left( {I_{L\; \_ 0} + I_{L\; \_ \; p}} \right) \times \frac{T_{off} + T_{on}}{T_{s}}} = {\frac{1}{2} \times {\left( {I_{L\; \_ 0} + I_{L\; \_ \; p}} \right).}}}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

As shown in FIG. 4(C), in CRM, the demagnetization period, T_(demag), isslightly shorter than the off-time of the switch, T_(off). Thedemagnetization process ends at point C, and the next switching cyclestarts shortly after the completion of the demagnetization process. Thenext switching cycle starts at a minimum voltage level (e.g., a valley)of the drain voltage of a MOS transistor switch or at a minimum voltagelevel (e.g., a valley) of the collector voltage of a bipolar transistorswitch.

In CRM, the lamp current 392, which is equal to the average inductorcurrent, is determined as follows:

$\begin{matrix}{I_{out} = {\frac{1}{2} \times I_{L\; \_ \; p} \times {\frac{T_{demag} + T_{on}}{T_{s}}.}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

Since the demagnetization period, T_(demag), is approximately equal tothe off-time of the switch 320, T_(off), and the initial magnitude ofthe inductor current (e.g., I_(L)) at the beginning of the on-time ofthe switch 320 is equal to zero,

$\begin{matrix}{{I_{out} \approx {\frac{1}{2} \times I_{L\; \_ \; p} \times \frac{T_{off} + T_{on}}{T_{s}}}} = {\frac{1}{2} \times {I_{L\; \_ \; p}.}}} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

Referring to FIG. 3, the lamp current 392 is the averaged magnitude ofthe inductor current (e.g., I_(L)) in each switching cycle as follows:

$\begin{matrix}{I_{out} = {\frac{1}{T} \times {\int_{0}^{T}{{I_{L}(t)}\ {dt}}}}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$

where T represents an integration period, and I_(L) represents theinductor current that flows through the inductor 340. For example, T isequal to or larger than T_(s), which represents the switching period.

According to one embodiment, to achieve

I _(out) =I _(c)  (Equation 7)

the following can be obtained with Equation 6:

∫₀ ^(T) I _(L)(t)dt=I _(c) ×T=∫ ₀ ^(T) I _(c) dt  (Equation 8)

where I_(c) represents a constant current magnitude.

In another embodiment, in practice, if

|∫₀ ^(T) I _(L)(t)dt−∫ ₀ ^(T) I _(c) dt|<C(Equation 9)

where C is a predetermined threshold, then the constant lamp current 392can be achieved or substantially achieved.

Referring to FIGS. 4(A), (B), and (C), as discussed above, the lampcurrent 392 is determined according to Equation 2, Equation 3, andEquation 4, for DCM, CCM and CRM, respectively. Additionally, for CCMand CRM,

$\begin{matrix}{I_{out} = {{\frac{1}{T_{s}} \times {\int_{0}^{T_{s}}{{I_{L}(t)}\ {dt}}}} = {\frac{1}{T_{on}} \times {\int_{0}^{T_{on}}{{I_{L}(t)}{{dt}.}}}}}} & \left( {{Equation}\mspace{14mu} 10} \right)\end{matrix}$

Also referring to FIG. 3, the inductor current I_(L) during the on-timeof the switch 320 as shown in Equation 10 is converted by the sensingresistor 360 into the current sensing signal 314, which is received bythe PWM controller 310 through the terminal 374.

According to another embodiment, for DCM, CCM and CRM,

(I _(L) _(_) _(p)(i)+I _(L) _(_) ₀(i))×(T _(demag)(i)+T _(on)(i))=I_(c)(i)×T _(s)(i)  (Equation 11A)

or

(2×I _(L) _(_) _(Ton/2)(i))×(T _(demag)(i)+T _(on)(i))=I _(c)(i)×T_(s)(i)  (Equation 11B)

where i corresponds to the i^(th) switching cycle. Additionally, I_(L)_(_) _(Ton/2) represents the magnitude of the inductor current (e.g.,I_(L)) at the middle of the on-time of the switch 320.

Also, since in CCM, the next switching cycle starts before thedemagnetization process is completed, the actual length of thedemagnetization process before the next switching cycle starts islimited to the off-time of the switch; hence T_(off) can be representedby T_(demag) in CCM.

For example, if

$\begin{matrix}{{{Limit}_{N\rightarrow\infty}{\left( {{\sum\limits_{i = 0}^{N}{\left( {{I_{L\; \_ \; p}(i)} + {I_{L\; \_ \; 0}(i)}} \right) \times \left( {{T_{demag}(i)} + {T_{on}(i)}} \right)}} - {\sum\limits_{i = 0}^{N}{{I_{c}(i)} \times {T_{s}(i)}}}} \right)}} < {C\mspace{14mu} {or}}} & \left( {{Equation}\mspace{14mu} 12A} \right) \\{{{Limit}_{N\rightarrow\infty}{\left( {{\sum\limits_{i = 0}^{N}{\left( {2 \times {I_{L\; \_ \; {{Ton}/2}}(i)}} \right) \times \left( {{T_{demag}(i)} + {T_{on}(i)}} \right)}} - {\sum\limits_{i = 0}^{N}{{I_{c}(i)} \times {T_{s}(i)}}}} \right)}} < C} & \left( {{Equation}\mspace{14mu} 12B} \right)\end{matrix}$

where C is a predetermined threshold, then the constant lamp current canbe achieved.

In another example, Equation 12A is rewritten into an integration formatas follows:

|∫[I _(L) _(_) _(p)(i)+I _(L) _(_) ₀(i)]×[U(t−T _(s)(i))−U(t−T _(s)(i)−T_(demag)(i))]dt−∫I _(c)(t)dt|<C  (Equation 13)

where U(t) is the unit step function, and I_(c)(t) is equal to aconstant I_(c) _(_) _(ref). Hence, in the steady state, the followingcan be obtained:

|∫[I _(L) _(_) _(p)(i)+I _(L) _(_) ₀(i)]×[U(t−T _(s)(i))−U(t−T _(s)(i)−T_(demag)(i))]dt−∫I _(c) _(_) _(ref) dt|<C  (Equation 14A)

In yet another example, Equation 12B can be rewritten into anintegration format, and hence, in the steady state, the following can beobtained:

|∫[2×I _(L) _(_) _(Ton/2) ]×[U(t−T _(s)(i))−U(t−T _(s)(i)−T_(demag)(i))]dt−∫I _(c) _(_) _(ref) dt|<C  (Equation 14B)

In one embodiment, referring to Equations 2, 3 and 4, for DCM, CCM andCRM,

$\begin{matrix}{I_{out} = {\frac{1}{2} \times \left( {I_{L\; \_ \; 0} + L_{L\; \_ \; p}} \right) \times \frac{T_{demag} + T_{on}}{T_{s}}}} & \left( {{Equation}\mspace{14mu} 15} \right)\end{matrix}$

where T_(demag) represents T_(off) for CCM, and I_(L) _(_) ₀ is equal tozero for DCM and CRM.

For example, if the lamp current 392 is maintained at a constant level,e.g.,

$\begin{matrix}{{I_{out} = {\frac{1}{2} \times I_{ref}}}{then}} & \left( {{Equation}\mspace{14mu} 16} \right) \\{{\left( {L_{L\; \_ \; p} + I_{L\; \_ \; 0}} \right) \times \frac{T_{demag} + T_{on}}{T_{s}}} = I_{ref}} & \left( {{Equation}\mspace{14mu} 17} \right)\end{matrix}$

where I_(ref) represents a constant current level. Hence,

(I _(L) _(_) _(p) +I _(L) _(_) ₀)×(T _(demag) +T _(on))=I _(ref) ×T_(s)  (Equation 18).

In another example, T_(s), T_(demag), and T_(on) may vary from oneswitching cycle to another switching cycle, so for the ith switchingcycle, the following may be obtained:

(I _(L) _(_) _(p)(i)+I _(L) _(_) ₀(i))×(T _(demag)(i)+T _(on)(i))≠I_(ref) ×T _(s)(i)  (Equation 19)

But if

$\begin{matrix}{{{Limit}_{N\rightarrow\infty}{\left( {{\sum\limits_{i = 0}^{N}{\left( {{I_{L\; \_ \; p}(i)} + {I_{L\; \_ \; 0}(i)}} \right) \times \left( {{T_{demag}(i)} + {T_{on}(i)}} \right)}} - {\sum\limits_{i = 0}^{N}{I_{ref} \times {T_{s}(i)}}}} \right)}} < A} & \left( {{Equation}\mspace{14mu} 20A} \right)\end{matrix}$

where A represents a predetermined threshold, the following integrationformat can be obtained:

|∫(I _(L) _(_) _(p)(i)+I _(L) _(_) ₀(i))×[U(t−T _(s)(i))−U(t−T _(s)(i)−T_(on)(i)−T _(demag)(i))]dt−∫I _(ref) dt|<A  (Equation 21A)

where U(t) is the unit step function.

In yet another example, if

$\begin{matrix}{{{Limit}_{N\rightarrow\infty}{\left( {{\sum\limits_{i = 0}^{N}{\left( {2 \times {I_{L\; \_ \; {{Ton}/2}}(i)}} \right) \times \left( {{T_{demag}(i)} + {T_{on}(i)}} \right)}} - {\sum\limits_{i = 0}^{N}{I_{ref} \times {T_{s}(i)}}}} \right)}} < A} & \left( {{Equation}\mspace{14mu} 20B} \right)\end{matrix}$

where A represents a predetermined threshold, the following integrationformat can be obtained:

|∫(2×I _(L) _(_) _(Ton/2)(i))×[U(t−T _(s)(i))−U(t−T _(s)(i)−T _(on)(i)−T_(demag)(i))]dt−∫I _(ref) dt|  (Equation 21B)

where U(t) is the unit step function.

According to yet another embodiment, if Equations 20A and 21A aresatisfied and/or Equations 20B and 21B are satisfied, the lamp current392 is maintained at a constant level, regardless of the lamp voltage,the inductance of the inductor 340, and/or the input voltage 332.

For example, referring to FIG. 3, when the switch 320 is turned on(e.g., during T_(on)), the current that flows through the inductor 340(e.g. I_(L)) is sensed by the sensing resistor 360, which generates thecurrent sensing signal 314 (e.g., V_(cs)) as follows:

V _(cs) =I _(L) ×R _(s)  (Equation 22)

where V_(cs) represents the current sensing signal 314, I_(L) representsthe current that flows through the inductor 340, and R_(s) representsthe resistance of the sensing resistor 360.

In another example, based on Equations 21(A) and 22, one can obtain thefollowing:

$\begin{matrix}{{{\frac{1}{R_{s}}{\int{\left( {{V_{{cs}\; \_ \; p}(i)} + {I_{{cs}\; \_ \; 0}(i)}} \right) \times {\quad{{\left\lbrack {{U\left( {t - {T_{s}(i)}} \right)} - {U\left( {t - {T_{s}(i)} - {T_{on}(i)} - {T_{demag}(i)}} \right)}} \right\rbrack {dt}} - {\int{I_{ref}{dt}}}}}}}} < A}} & \left( {{Equation}\mspace{14mu} 23A} \right)\end{matrix}$

where V_(cs) _(_) _(p) represents the peak magnitude of the currentsensing signal 314, and corresponds to the peak magnitude of theinductor current at the end of the on-time of the switch 320.Additionally, V_(cs) _(_) ₀ represents the initial magnitude of thecurrent sensing signal 314, and corresponds to the initial magnitude ofthe inductor current at the beginning of the on-time of the switch 320.

In yet another example, based on Equations 21(B) and 22, one can obtainthe following:

$\begin{matrix}{{{\frac{1}{R_{s}}{\int{\left( {2 \times {V_{{cs}\; \_ \; {{Ton}/2}}(i)}} \right) \times {\quad{{\left\lbrack {{U\left( {t - {T_{s}(i)}} \right)} - {U\left( {t - {T_{s}(i)} - {T_{on}(i)} - {T_{demag}(i)}} \right)}} \right\rbrack {dt}} - {\int{I_{ref}{dt}}}}}}}} < A}} & \left( {{Equation}\mspace{14mu} 23B} \right)\end{matrix}$

where V_(cs) _(_) _(Ton/2) represents the magnitude of the currentsensing signal 314 at the middle of the on-time of the switch 320.

As discussed above and further emphasized here, FIG. 3 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, FIG. 3 is implemented according to FIG.5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, FIG. 10, FIG. 11, and/or FIG. 12. Inanother example, the leading-edge-blanking component 308 is removed, andthe current sensing signal 314 (e.g., V_(cs)) is received by theover-current-protection (OCP) component 384 through the terminal 374without going through the leading-edge-blanking component 308.

FIG. 5 is a simplified diagram for a LED lighting system according toanother embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. The lighting system 500 includes a switch 420, adiode 430, an inductor 440, capacitors 450 and 452, and a sensingresistor 460. Additionally, the lighting system 500 also includescycle-by-cycle processing components 520 and 522, a capacitor 530, asignal conditioning component 532, a transconductance amplifier 540, acomparator 542, a demagnetization detection component 544, aleading-edge blanking component 550, a flip-flop component 554, a clockgenerator 556, and a driver component 558.

For example, the switch 420, the diode 430, the inductor 440, thecapacitor 450, and the sensing resistor 460 are the same as the powerswitch 120, the diode 130, the inductor 140, the capacitor 150, and thesensing resistor 160, respectively. In another example, thecycle-by-cycle processing components 520 and 522, the signalconditioning component 532, the transconductance amplifier 540, thecomparator 542, the demagnetization detection component 544, theleading-edge blanking component 550, the flip-flop component 554, theclock generator 556, and the driver component 558 are located on a chip510. In yet another example, the capacitor 530 is located off the chip510. In yet another example, the chip 510 includes terminals 512, 514,516, 518, and 519.

As shown in FIG. 5, the lighting system 500 receives an input voltage534 and provides a lamp current 592 (e.g., an output current) and a lampvoltage to one or more LEDs 590. According to one embodiment, during theon-time of the switch 420 (e.g., T_(on)), a current that flows throughthe inductor 440 and the switch 420 is sensed by the resistor 460. Forexample, the resistor 460 generates, through the terminal 514 and withthe leading-edge blanking component 550, a current sensing signal 552.In another example, during the on-time of the switch 420 (e.g., T_(on)),the current sensing signal 552 is as follows:

V _(cs) =I _(L) ×R _(s)  (Equation 24)

where V_(cs) represents the current sensing signal 552, I_(L) representsthe current that flows through the inductor 440, and R_(s) representsthe resistance of the resistor 460.

In yet another example, combining Equations 20A and 24, the following isobtained:

$\begin{matrix}{{{Limit}_{N\rightarrow\infty}{\left( {{\frac{1}{R_{s}}{\sum\limits_{i = 0}^{N}{\left( {{V_{{cs}\; \_ \mspace{11mu} p}(i)} + {V_{{cs}\; \_ \; 0}(i)}} \right) \times \left( {{T_{demag}(i)} + {T_{on}(i)}} \right)}}} - {\sum\limits_{i = 0}^{N}{I_{ref} \times {T_{s}(i)}}}} \right)}} < A} & \left( {{Equation}\mspace{14mu} 25A} \right)\end{matrix}$

where A represents a predetermined threshold, and I_(ref) represents apredetermined referenced current. Additionally, V_(cs) _(_) _(p)represents the peak magnitude of the current sensing signal 552, which,for example, corresponds to the peak magnitude of the inductor currentat the end of the on-time of the switch 420. Moreover, V_(cs) _(_) ₀represents the initial magnitude of the current sensing signal 552,which, for example, corresponds to the initial magnitude of the inductorcurrent at the beginning of the on-time of the switch 420. Also, T_(s)represents the switching period of the switch 420, and T_(on) representsthe on-time of the switch 420. Additionally, T_(demag) represents thedemagnetization period for DCM and CRM, and T_(demag) represents theoff-time of the switch 420 (e.g., T_(off)) for CCM.

In yet another example, combining Equations 20B and 24, the following isobtained:

$\begin{matrix}{{{Limit}_{N\rightarrow\infty}{\left( {{\frac{1}{R_{s}}{\sum\limits_{i = 0}^{N}{\left( {2 \times {V_{{cs}\; \_ \; {{Ton}/2}}(i)}} \right) \times \left( {{T_{demag}(i)} + {T_{on}(i)}} \right)}}} - {\sum\limits_{i = 0}^{N}{I_{ref} \times {T_{s}(i)}}}} \right)}} < A} & \left( {{Equation}\mspace{14mu} 25B} \right)\end{matrix}$

where A represents a predetermined threshold, and I_(ref) represents apredetermined referenced current. Additionally, V_(cs) _(_) _(Ton/2)represents the magnitude of the current sensing signal 552 at the middleof the on-time of the switch 420. Also, T_(s) represents the switchingperiod of the switch 420, and T_(on) represents the on-time of theswitch 420. Additionally, T_(demag) represents the demagnetizationperiod for DCM and CRM, and T_(demag) represents the off-time of theswitch 420 (e.g., T_(off)) for CCM.

According to some embodiments, the current sensing signal 552 isreceived by the cycle-by-cycle processing component 520. In oneembodiment, for each switching cycle, the processing component 520generates a signal 521 that is equal to (I_(L) _(_) _(p)+I_(L) _(_)₀)×(T_(on)+T_(demag)). In another embodiment, for each switching cycle,the processing component 520 generates a signal 521 that is equal to(I_(L) _(_) _(p)+I_(L) _(_) _(p))×(T_(on))+(2×I_(L) _(_)_(Ton/2))×(T_(demag)).

For example, for each switching cycle, the average inductor currentduring the on-time of the switch 420 (e.g., T_(on)) is determineddirectly based on the sensed current 552 as ½(I_(L) _(_) _(p)+I_(L) _(_)₀) when the switch 420 is closed. In another example, for each switchingcycle, the average inductor current during the demagnetization period(e.g., T_(demag)) is determined indirectly based on the sensed current552 at the middle of the on-time as I_(L) _(_) _(Ton/2) which is sampledwhen the switch 420 is closed and then held by the cycle-by-cycleprocessing component 520. In yet another example, for each switchingcycle, the average inductor current during the off-time (e.g., T_(off))is determined indirectly based on the sensed current 552 at the middleof the on-time as (I_(L) _(_) _(Ton/2))×(T_(demag))/(T_(off)), and I_(L)_(_) _(Ton/2) is sampled when the switch 420 is closed and then held bythe cycle-by-cycle processing component 520. For DCM and CRM, thedemagnetization period (e.g., T_(demag)) represents duration of thedemagnetization process, but for CCM, the demagnetization period (e.g.,T_(demag)) represents duration of the off-time according to certainembodiments.

In yet another example, for each switching cycle, the processingcomponent 522 generates a signal 523 that is equal to I_(ref)×T_(s). Inyet another example, the demagnetization detection component 544receives a feedback signal 564 from the capacitor 452, and generates aDemag signal 545. The Demag signal 545 has a pulse width of T_(demag)for each switching cycle.

According to another embodiment, the signals 523 and 521 are received bythe transconductance amplifier 540. For example, the magnitudedifference of I_(ref)×T_(s)−(I_(L) _(_) _(p)+I_(L) _(_)₀)×(T_(on)+T_(demag)) is amplified and integrated by thetransconductance amplifier 540 and the capacitor 530 as part of thepractical implementation of Equation 25A. In another example, themagnitude difference of I_(ref)×T_(s)−└(I_(L) _(_) _(p)+I_(L) _(_)₀)×(T_(on))+(2×I_(L) _(_) _(Ton/2))×(T_(demag))┘ is amplified andintegrated by the transconductance amplifier 540 and the capacitor 530as part of the practical implementation of Equation 25B. In anotherexample, the transconductance amplifier 540 and the capacitor 530 forman integrator, which generates a signal 531 that is received by thecomparator 542 directly or indirectly through the signal conditioningcomponent 532.

According to yet another embodiment, the comparator 542 also receivesthe current sensing signal 552, and in response generates a comparisonsignal 543. For example, the comparison signal 543 is received by theflip-flop component 554, and the flip-flop component 554 also receives aclock signal 555 from the clock generator 556 and generates a modulationsignal 557. In another example, the modulation signal 557 is received bythe driver component 558, which in response generates the drive signal559.

In one embodiment, the drive signal 559 is sent to the switch 420through the terminal 512, and is also received by the cycle-by-cycleprocessing component 520. In another embodiment, the signal 531 is usedto adjust the pulse width of the drive signal 559 with pulse-widthmodulation.

As discussed above and further emphasized here, FIG. 5 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the signal conditioning component 532 isremoved, and the signal 531 is received directly by the comparator 542.In another example, the leading-edge blanking component 550 is removed,and the signal 552 is received directly from the terminal 514. In yetanother example, the capacitor 530 is located on the chip 510. In yetanother example, for CRM, the clock generator 556 is replaced by a pulsesignal generator, which receives the Demag signal 545 and in responsegenerates pulses of a pulse signal 555. In yet another example, thepulse signal 555 is received by the flip-flop component 554, anddifferent pulses of the pulse signal 555 correspond to differentswitching cycles.

FIG. 6 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention. This diagram is merelyan example, which should not unduly limit the scope of the claims. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications. The lighting system 600 includes aswitch 4620, a diode 4630, an inductor 4640, capacitors 4650 and 4652,and a sensing resistor 4660. Additionally, the lighting system 600 alsoincludes a comparator 642, a demagnetization detection component 644, aleading-edge blanking component 650, a flip-flop component 654, a clockgenerator 656, and a driver component 658. Moreover, the lighting system600 also includes sampling-and-holding components 662 and 664,voltage-to-current converters 660, 666 and 668, a switch 680, and acapacitor 690. Also, the lighting system 600 further includes a signalamplifier 686, a voltage-to-current converter 688, and a switch 682.

For example, the switch 4620, the diode 4630, the inductor 4640, thecapacitor 4650, and the sensing resistor 4660 are the same as the powerswitch 120, the diode 130, the inductor 140, the capacitor 150, and thesensing resistor 160, respectively. In another example, the comparator642, the demagnetization detection component 644, the leading-edgeblanking component 650, the flip-flop component 654, the clock generator656, the driver component 658, the sampling-and-holding components 662and 664, the voltage-to-current converters 660, 666 and 668, the switch680, the signal amplifier 686, the voltage-to-current converter 688, andthe switch 682 are located on a chip 610. In yet another example, thecapacitor 690 is located off the chip 610. In yet another example, thechip 610 includes terminals 612, 614, 616, 618, and 619.

According to one embodiment, in CCM, the next switching cycle startsbefore the demagnetization process is completed. For example, the actuallength of the demagnetization process (e.g., T_(demag)) before the nextswitching cycle starts is limited to the off-time of the switch 4620(e.g., T_(off)); hence T_(off) can be represented by T_(demag) in CCM.According to another embodiment, in DCM, the off-time of the switch 4620(e.g., T_(off)) is much longer than the demagnetization period (e.g.,T_(demag)). According to yet another embodiment, in CRM, the off-time ofthe switch 4620 (e.g., T_(off)) is slightly longer than thedemagnetization period (e.g., T_(demag)).

As shown in FIG. 6, the lighting system 600 receives an input voltage632 and provides a lamp current 692 (e.g., an output current) and a lampvoltage to one or more LEDs 4690. In one embodiment, a current thatflows through the inductor 4640 is sensed by the resistor 4660. Forexample, the resistor 4660 generates, through the terminal 614 and withthe leading-edge blanking component 650, a current sensing signal 652.

In another embodiment, the sampling-and-holding component 662 receivesat least a drive signal 659 and a control signal 661. For example, thecontrol signal 661 includes, for each switching cycle, a pulse that hasa rising edge at the beginning of the on-time of the switch 4620 (e.g.,at the rising edge of the drive signal 659). In another example, duringthe pulse, the current sensing signal 652 (e.g., V_(cs)) is sampled andheld as a voltage signal 663 (e.g., V_(s2)). In yet another example,after the falling edge of the pulse, the voltage signal 663 remainsconstant (e.g., being equal to V_(cs) _(_) ₀) until the next pulse ofthe control signal 661. In one embodiment, the pulse of the controlsignal 661 is so narrow that V_(cs) _(_) ₀ equals approximately and thusrepresents the current sensing signal 652 at the beginning of theon-time of the switch 4620.

In yet another embodiment, the sampling-and-holding component 664receives at least the drive signal 659, which includes, for eachswitching cycle, a pulse that has a width corresponding to the on-timeof the switch 4620 (e.g., T_(on)). For example, during the pulse of thedrive signal 659, the current sensing signal 652 (e.g., V_(cs)) issampled and held as a voltage signal 665 (e.g., V_(s3)). In anotherexample, after the falling edge of the pulse, the voltage signal 665remains constant (e.g., being equal to V_(cs) _(_) _(p)) until the nextpulse of the drive signal 659.

As shown in FIG. 6, the voltage signals 663 and 665 are received by thevoltage-to-current converters 666 and 668, which in response generatecurrent signals 667 and 669, respectively, according to one embodiment.For example, the current signal 667 is represented by I_(s2), and thecurrent signal 669 is represented by I_(s3). In another example, the sumof the current signals 667 and 669 forms a sinking current 681 (e.g.,I_(sink2)), which is used to discharge the capacitor 690 if the switch680 is closed.

According to another embodiment, the switch 680 is controlled by a Demagsignal 645, which is generated by the demagnetization detectioncomponent 644. For example, if the Demag signal 645 is at the logic highlevel, the switch 680 is closed. In another example, the switch 680 isclosed during the demagnetization period and is open during the rest ofthe switching period. In yet another example, the sinking current 681discharges the capacitor 690 during the demagnetization period (e.g.,during T_(demag)).

Also, as shown in FIG. 6, the signal amplifier 686 receives the currentsensing signal 652 (e.g., V_(cs)) and generates a voltage signal 687(e.g., V_(s1)) according to one embodiment. For example, the voltagesignal 687 (e.g., V_(s1)) equals two times the current sensing signal652 (e.g., V_(cs)) in magnitude. According to another embodiment, thevoltage signal 687 is received by the voltage-to-current converter 688,which in response generates a sinking current 689 (e.g., I_(sink1)). Forexample, the sinking current 689 is used to discharge the capacitor 690if the switch 682 is closed.

According to yet another embodiment, the switch 682 is controlled by asignal 685, which has been generated based on the signal 659. Forexample, if the signal 685 is at the logic high level, the switch 682 isclosed, and if the signal 685 is at the logic low level, the switch 682is open. In another example, the switch 682 is closed during the on-timeof the switch 4620, and is open during the off-time of the switch 4620.In yet another example, the sinking current 689 discharges the capacitor690 during the on-time of the switch 4620. According to yet anotherembodiment, the voltage-to-current converter 660 receives apredetermined voltage signal 691 (e.g., V_(ref)), and in responsegenerates a charging current 661 (e.g., I_(ref)). For example, thecharging current 661 charges the capacitor 690 during the switchingperiod (e.g., during T_(s)). According to yet another embodiment, thesignal 683 (e.g., V_(C)) is generated by the charging current 661 (e.g.,I_(ref)), the discharging current 681 (e.g., I_(sink2)), and thedischarging current 689 (e.g., I_(sink1)) for the capacitor 690. Forexample, the signal 683 (e.g., V_(C)) decreases in magnitude during thedemagnetization period (e.g., during T_(demag)), and increases duringthe rest of the switching cycle.

In one embodiment, the comparator 642 receives the signal 683 (e.g.,V_(C)) and also receives the current sensing signal 652 through theslope compensation component 684. For example, in response, thecomparator 642 generates a comparison signal 643, which is received bythe flip-flop component 654. In another example, the flip-flop component654 also receives a clock signal 655 from the clock generator 656 andgenerates a modulation signal 657. In yet another example, themodulation signal 657 is received by the driver component 658, which inresponse outputs the drive signal 659 to the switch 4620 and thesampling-and-holding components 662 and 664.

According to one embodiment, for CCM, DCM and CRM,

I _(s2) =α×V _(cs) _(_) ₀ =α×I _(L) _(_) ₀ ×R _(s)  (Equation 26)

and

I _(s3) =α×V _(cs) _(_) _(p) =α×I _(L) _(_) _(p) ×R _(s)  (Equation 27).

Hence

I _(sink2) =I _(s2) +I _(s3) =α×I _(L) _(_) ₀ ×R _(s) +α×I _(L) _(_)_(p) ×R _(s)  (Equation 28).

Additionally,

I _(sink1)=2×α×V _(cs)  (Equation 29)

where α is a constant related to the voltage-to-current converters 666,668 and 688, and R_(s) is the resistance of the sensing resistor 4660.

According to another embodiment, if, within each switching cycle, thecharging and the discharging of the capacitor 690 are equal, thelighting system 600 reaches the equilibrium (e.g., the steady state), asfollows:

I _(ref) ×T _(s)=½×I _(sink1) _(_) _(p) ×T _(on) +I _(sink2) ×T_(demag)  (Equation 30)

where

I _(sink1) _(_) _(p)=2×α×V _(cs) _(_) _(p)  (Equation 31).

Combining Equations 28-31, the following can be obtained:

$\begin{matrix}{I_{ref} = {\alpha \times R_{s} \times \left( {I_{L\; \_ \; 0} + I_{L\; \_ \; p}} \right) \times {\frac{\left( {T_{on} + T_{demag}} \right)}{T_{s}}.}}} & \left( {{Equation}\mspace{14mu} 32A} \right) \\{{{If}\mspace{14mu} I_{ref}} = {\beta \times V_{ref}}} & \left( {{Equation}\mspace{14mu} 33A} \right) \\{{\left( {I_{L\; \_ \; 0} + I_{L\; \_ \; p}} \right) \times \frac{\left( {T_{on} + T_{demag}} \right)}{T_{s}}} = \frac{\beta \times V_{ref}}{\alpha \times R_{s}}} & \left( {{Equation}\mspace{14mu} 34A} \right)\end{matrix}$

where β is a constant related to the voltage-to-current converter 660.

$\begin{matrix}{{{Since}\mspace{14mu} I_{out}} = {\frac{1}{2} \times \left( {I_{L\; \_ \; 0} + I_{L\; \_ \; p}} \right) \times \frac{T_{demag} + T_{on}}{T_{s}}}} & \left( {{Equation}\mspace{14mu} 35A} \right) \\{{{then}\mspace{14mu} I_{out}} = {\frac{\beta}{2 \times \alpha \times R_{s}} \times V_{ref}}} & \left( {{Equation}\mspace{14mu} 36A} \right)\end{matrix}$

where I_(out) represents the lamp current 692. According to yet anotherembodiment, α, β, R_(s), and V_(ref) are all constants, so the constantlamp current 692 is achieved.

As discussed above and further emphasized here, FIG. 6 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. In one embodiment, the leading-edge blankingcomponent 650 is removed, and the signal 652 is received directly fromthe terminal 614. In another embodiment, the capacitor 690 is located onthe chip 610. In yet another embodiment, a low-pass filter and/or abuffer are added to process the signal 683 before the signal 683 isreceived by the comparator 642. For example, a voltage divider (e.g.,formed by two resistors) is further added to divide the processed signal683 before the processed signal 683 is received by the comparator 642.

According to another embodiment, for DCM and CRM, V_(cs) _(_) ₀ is equalto zero, so the sampling-and-holding component 662 and thevoltage-to-current converter 666 are removed if the lighting system 600does not need to operate in CCM for constant lamp current 692. Accordingto yet another embodiment, for CRM, the clock generator 656 is replacedby a pulse signal generator, which receives the Demag signal 645 and inresponse generates pulses of a pulse signal 655. For example, the pulsesignal 655 is received by the flip-flop component 654, and differentpulses of the pulse signal 655 correspond to different switching cycles.

According to yet another embodiment, the lighting system 600 is modifiedso that the following can be obtained:

$\begin{matrix}{I_{ref} = {\alpha \times R_{s} \times \left( {2 \times I_{L\; \_ \; {{Ton}/2}}} \right) \times {\frac{\left( {T_{on} + T_{demag}} \right)}{T_{s}}.}}} & \left( {{Equation}\mspace{14mu} 32B} \right) \\{{{If}\mspace{14mu} I_{ref}} = {\beta \times V_{ref}}} & \left( {{Equation}\mspace{14mu} 33B} \right) \\{{\left( {2 \times I_{L\; \_ \; {{Ton}/2}}} \right) \times \frac{\left( {T_{on} + T_{demag}} \right)}{T_{s}}} = \frac{\beta \times V_{ref}}{\alpha \times R_{s}}} & \left( {{Equation}\mspace{14mu} 34B} \right)\end{matrix}$

where β is a constant related to the voltage-to-current converter 660.

$\begin{matrix}{{{Since}\mspace{14mu} I_{out}} = {\left( I_{L\; \_ \; {{Ton}/2}} \right) \times \frac{T_{demag} + T_{on}}{T_{s}}}} & \left( {{Equation}\mspace{14mu} 35B} \right) \\{{{then}\mspace{14mu} I_{out}} = {\frac{\beta}{2 \times \alpha \times R_{s}} \times V_{ref}}} & \left( {{Equation}\mspace{14mu} 36B} \right)\end{matrix}$

where I_(out) represents the lamp current 692. α, β, R_(s), and V_(ref)are all constants, so the constant lamp current 692 is achievedaccording to certain embodiments.

FIG. 7 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention. This diagram is merelyan example, which should not unduly limit the scope of the claims. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications. The lighting system 700 includes aswitch 4720, a diode 4730, an inductor 4740, a capacitor 4750, and asensing resistor 4760. Additionally, the lighting system 700 alsoincludes a comparator 742, a leading-edge blanking component 750, aflip-flop component 754, a clock generator 756, and a driver component758. Moreover, the lighting system 700 also includes voltage-to-currentconverters 760 and 788, switches 780 and 782, a capacitor 790, and asignal amplifier 786.

For example, the switch 4720, the diode 4730, the inductor 4740, thecapacitor 4750, and the sensing resistor 4760 are the same as the powerswitch 120, the diode 130, the inductor 140, the capacitor 150, and thesensing resistor 160, respectively. In another example, the comparator742, the leading-edge blanking component 750, the flip-flop component754, the clock generator 756, the driver component 758, thevoltage-to-current converters 760 and 788, the switches 780 and 782, andthe signal amplifier 786 are located on a chip 710. In yet anotherexample, the capacitor 790 is located off the chip 710. In yet anotherexample, the chip 710 includes terminals 712, 714, 718, and 719.

As shown in FIG. 7, the lighting system 700 receives an input voltage732 and provides a lamp current 792 (e.g., an output current) and a lampvoltage to one or more LEDs 4790. In one embodiment, a current thatflows through the inductor 4740 is sensed by the resistor 4760. Forexample, the resistor 4760 generates, through the terminal 714 and withthe leading-edge blanking component 750, a current sensing signal 752.

In another embodiment, the signal amplifier 786 receives the currentsensing signal 752 (e.g., V_(cs)) and generates a voltage signal 787(e.g., V_(s1)). For example, the voltage signal 787 (e.g., V_(s1))equals two times the current sensing signal 752 (e.g., V_(cs)) inmagnitude. In yet another embodiment, the gain of the signal amplifier786 is G (e.g. G being a predetermined positive number). In yet anotherembodiment, the voltage signal 787 is received by the voltage-to-currentconverter 788, which in response generates a sinking current 789 (e.g.,I_(sink1)). For example, the sinking current 789 is used to dischargethe capacitor 790 if the switch 782 is closed. In another example, theswitch 782 is controlled by a signal 785, which has been generated basedon a drive signal 759.

In yet another embodiment, the voltage-to-current converter 760 receivesa predetermined voltage signal 791 (e.g., V_(ref)), and in responsegenerates a charging current 761 (e.g., I_(ref)). For example, thecharging current 761 is used to charge the capacitor 790 if the switch780 is closed. In another example, the switch 780 is controlled by thesignal 785, which has been generated based on the drive signal 759.

According to one embodiment, if the signal 785 is at the logic highlevel, the switches 780 and 782 are closed, and if the signal 785 is atthe logic low level, the switches 780 and 782 are open. For example, theswitches 780 and 782 are closed during the on-time of the switch 4720,and are open during the off-time of the switch 4720. In another example,the sinking current 789 discharges the capacitor 790 and the chargingcurrent 761 charges the capacitor 790 during the on-time of the switch4720. According to another embodiment, the signal 783 (e.g., V_(C)) isgenerated by the charging current 761 (e.g., I_(ref)) and thedischarging current 789 (e.g., I_(sink1)) for the capacitor 790.

As shown in FIG. 7, the comparator 742 receives the signal 783 (e.g.,V_(C)) and also receives the current sensing signal 752 through theslope compensation component 784. For example, in response, thecomparator 742 generates a comparison signal 743, which is received bythe flip-flop component 754. In another example, the flip-flop component754 also receives a clock signal 755 from the clock generator 756 andgenerates a modulation signal 757. In yet another example, themodulation signal 757 is received by the driver component 758, which inresponse outputs the drive signal 759 to the switch 4720.

According to one embodiment, for CCM, since

$\begin{matrix}{\; {I_{out} = {{\frac{1}{T_{s}} \times {\int_{0}^{T_{s}}{{I_{L}(t)}{dt}}}} = {\frac{1}{T_{on}} \times {\int_{0}^{T_{on}}{{I_{L}(t)}{dt}}}}}}} & \left( {{Equation}\mspace{14mu} 37} \right) \\{{{then}\mspace{14mu} I_{out}} = \frac{V_{ref}}{R_{s}}} & \left( {{Equation}\mspace{14mu} 38} \right)\end{matrix}$

where I_(out) represents the lamp current 792 and R_(s) is theresistance of the sensing resistor 4760. According to anotherembodiment, R_(s) and V_(ref) are all constants, so the constant lampcurrent 792 is achieved.

As discussed above and further emphasized here, FIG. 7 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the leading-edge blanking component 750is removed, and the signal 752 is received directly from the terminal714. In another example, the capacitor 790 is located on the chip 710.In yet another example, a low-pass filter and/or a buffer are added toprocess the signal 783 before the signal 783 is received by thecomparator 742. In yet another example, two resistors are further addedto divide the processed signal 783 before the processed signal 783 isreceived by the comparator 742.

FIG. 8 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention. This diagram is merelyan example, which should not unduly limit the scope of the claims. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications. The lighting system 800 includes aswitch 4820, a diode 4830, an inductor 4840, a capacitor 4850, and asensing resistor 4860. Additionally, the lighting system 800 alsoincludes a comparator 842, a leading-edge blanking component 850, aflip-flop component 854, a clock generator 856, and a driver component858. Moreover, the lighting system 800 also includes a transconductanceamplifier 886, switches 880 and 882, and a capacitor 890.

For example, the switch 4820, the diode 4830, the inductor 4840, thecapacitor 4850, and the sensing resistor 4860 are the same as the powerswitch 120, the diode 130, the inductor 140, the capacitor 150, and thesensing resistor 160, respectively. In another example, the comparator842, the leading-edge blanking component 850, the flip-flop component854, the clock generator 856, the driver component 858, thetransconductance amplifier 886, and the switches 880 and 882 are locatedon a chip 810. In yet another example, the capacitor 890 is located offthe chip 810. In yet another example, the chip 810 includes terminals812, 814, 818, and 819.

As shown in FIG. 8, the lighting system 800 receives an input voltage832 and provides a lamp current 892 (e.g., an output current) and a lampvoltage to one or more LEDs 4890. In one embodiment, a current thatflows through the inductor 4840 is sensed by the resistor 4860. Forexample, the resistor 4860 generates, through the terminal 814 and withthe leading-edge blanking component 850, a current sensing signal 852.

In another embodiment, the transconductance amplifier 886 receives thecurrent sensing signal 852 (e.g., V_(cs)), and also receives apredetermined voltage signal 891 (e.g., V_(ref)) through the switch 880.For example, the switch 880 is controlled by a signal 885, which hasbeen generated based on a drive signal 859. In another example, if thesignal 885 is at the logic high level, the switch 880 is closed, and ifthe signal 885 is at the logic low level, the switch 880 is open. In yetanother example, the switch 880 is closed during the on-time of theswitch 4820, and is open during the off-time of the switch 4820.

In yet another embodiment, during the on-time of the switch 4820, thetransconductance amplifier 886 compares the current sensing signal 852(e.g., V_(cs)) and the predetermined voltage signal 891 (e.g., V_(ref)),and converts the difference between the current sensing signal 852(e.g., V_(cs)) and the predetermined voltage signal 891 (e.g., V_(ref))into a current 889. For example, the current 889 is proportional to thedifference between the current sensing signal 852 (e.g., V_(cs)) and thepredetermined voltage signal 891 (e.g., V_(ref)). In another example,during the on-time of the switch 4820, the current 889 charges thecapacitor 890 if the predetermined voltage signal 891 (e.g., V_(ref)) islarger than the current sensing signal 852 (e.g., V_(cs)) in magnitude,and discharges the capacitor 890 if the predetermined voltage signal 891(e.g., V_(ref)) is smaller than the current sensing signal 852 (e.g.,V_(cs)) in magnitude.

In yet another embodiment, during the off-time of the switch 4820, thepredetermined voltage signal 891 (e.g., V_(ref)) is shorted to theground through the switch 882. For example, the switch 882 is controlledby a signal 845, which has been generated based on the drive signal 859.In another example, if the signal 845 is at the logic high level, theswitch 882 is closed, and if the signal 845 is at the logic low level,the switch 882 is open. In yet another example, the switch 882 is closedduring the off-time of the switch 4820, and is open during the on-timeof the switch 4820.

As shown in FIG. 8, a signal 883 (e.g., V_(C)) is generated by thecurrent 889 charging and/or discharging the capacitor 890. In oneembodiment, the comparator 842 receives the signal 883 (e.g., V_(C)) andalso receives the current sensing signal 852 through the slopecompensation component 884. For example, in response, the comparator 842generates a comparison signal 843, which is received by the flip-flopcomponent 854. In another example, the flip-flop component 854 alsoreceives a clock signal 855 from the clock generator 856 and generates amodulation signal 857. In yet another example, the modulation signal 857is received by the driver component 858, which in response outputs thedrive signal 859 to the switch 4820.

As discussed above and further emphasized here, FIG. 8 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the leading-edge blanking component 850is removed, and the signal 852 is received directly from the terminal814. In another example, the capacitor 890 is located on the chip 810.

FIG. 9 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention. This diagram is merelyan example, which should not unduly limit the scope of the claims. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications. The lighting system 900 includes aswitch 4920, a diode 4930, an inductor 4940, capacitors 4950 and 4952,and a sensing resistor 4960. Additionally, the lighting system 900 alsoincludes a comparator 942, a demagnetization detection component 944, aleading-edge blanking component 950, a flip-flop component 954, a pulsesignal generator 956, and a driver component 958. Moreover, the lightingsystem 900 also includes a transconductance amplifier 986, switches 980and 982, and a capacitor 990.

For example, the switch 4920, the diode 4930, the inductor 4940, thecapacitor 4950, and the sensing resistor 4960 are the same as the powerswitch 120, the diode 130, the inductor 140, the capacitor 150, and thesensing resistor 160, respectively. In another example, the comparator942, the demagnetization detection component 944, the leading-edgeblanking component 950, the flip-flop component 954, the pulse signalgenerator 956, the driver component 958, the transconductance amplifier986, and the switches 980 and 982 are located on a chip 910. In yetanother example, the capacitor 990 is located off the chip 910. In yetanother example, the chip 910 includes terminals 912, 914, 916, 918, and919.

As shown in FIG. 9, the lighting system 900 receives an input voltage932 and provides a lamp current 992 (e.g., an output current) and a lampvoltage to one or more LEDs 4990. In one embodiment, a current thatflows through the inductor 4940 is sensed by the resistor 4960. Forexample, the resistor 4960 generates, through the terminal 914 and withthe leading-edge blanking component 950, a current sensing signal 952.

In another embodiment, the transconductance amplifier 986 receives thecurrent sensing signal 952 (e.g., V_(cs)), and also receives apredetermined voltage signal 991 (e.g., V_(ref)) through the switch 980.For example, the switch 980 is controlled by a signal 985, which hasbeen generated based on a drive signal 959. In another example, if thesignal 985 is at the logic high level, the switch 980 is closed, and ifthe signal 985 is at the logic low level, the switch 980 is open. In yetanother example, the switch 980 is closed during the on-time of theswitch 4920, and is open during the off-time of the switch 4920.

In yet another embodiment, during the on-time of the switch 4920, thetransconductance amplifier 986 compares the current sensing signal 952(e.g., V_(cs)) and the predetermined voltage signal 991 (e.g., V_(ref)),and converts the difference between the current sensing signal 952(e.g., V_(cs)) and the predetermined voltage signal 991 (e.g., V_(ref))into a current 989. For example, the current 989 is proportional to thedifference between the current sensing signal 952 (e.g., V_(cs)) and thepredetermined voltage signal 991 (e.g., V_(ref)). In another example,during the on-time of the switch 4920, the current 989 charges thecapacitor 990 if the predetermined voltage signal 991 (e.g., V_(ref)) islarger than the current sensing signal 952 (e.g., V_(cs)) in magnitude,and discharges the capacitor 990 if the predetermined voltage signal 991(e.g., V_(ref)) is smaller than the current sensing signal 952 (e.g.,V_(cs)) in magnitude.

In yet another embodiment, during the off-time of the switch 4920, thepredetermined voltage signal 991 (e.g., V_(ref)) is shorted to theground through the switch 982. For example, the switch 982 is controlledby a signal 945, which has been generated based on the drive signal 959.In another example, if the signal 945 is at the logic high level, theswitch 982 is closed, and if the signal 945 is at the logic low level,the switch 982 is open. In yet another example, the switch 982 is closedduring the off-time of the switch 4920, and is open during the on-timeof the switch 4920.

As shown in FIG. 9, a signal 983 (e.g., V_(C)) is generated by thecurrent 989 charging and/or discharging the capacitor 990. In oneembodiment, the comparator 942 receives the signal 983 (e.g., V_(C)) andalso receives the current sensing signal 952. For example, in response,the comparator 942 generates a comparison signal 943, which is receivedby the flip-flop component 954. In another example, the flip-flopcomponent 954 also receives a pulse signal 955 from the pulse signalgenerator 956 and generates a modulation signal 957. In yet anotherexample, the modulation signal 957 is received by the driver component958, which in response outputs the drive signal 959 to the switch 4920.In another embodiment, the pulse signal generator 956 receives a Demagsignal 945 from the demagnetization detection component 944, and inresponse generates pulses of the pulse signal 955. For example,different pulses of the pulse signal 955 correspond to differentswitching cycles.

As discussed above and further emphasized here, FIG. 9 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the leading-edge blanking component 950is removed, and the signal 952 is received directly from the terminal914. In another example, the capacitor 990 is located on the chip 910.In yet another example, a slope compensation component is added, throughwhich the comparator 942 receives the current sensing signal 952.

FIG. 10 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention. This diagram is merelyan example, which should not unduly limit the scope of the claims. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications. The lighting system 1000 includes aswitch 5020, a diode 5030, an inductor 5040, capacitors 5050 and 5052,and a sensing resistor 5060. Additionally, the lighting system 1000 alsoincludes a comparator 1042, a demagnetization detection component 1044,a leading-edge blanking component 1050, a flip-flop component 1054, aclock generator 1056, and a driver component 1058. Moreover, thelighting system 1000 also includes sampling-and-holding components 1062and 1064, voltage-to-current converters 1060, 1066 and 1068, a switch1080, and a capacitor 1090. Also, the lighting system 1000 furtherincludes a signal amplifier 1086, a voltage-to-current converter 1088, aswitch 1082, a multiplier component 1096, and resistors 1098 and 1099.

For example, the switch 5020, the diode 5030, the inductor 5040, thecapacitor 5050, and the sensing resistor 5060 are the same as the powerswitch 120, the diode 130, the inductor 140, the capacitor 150, and thesensing resistor 160, respectively. In another example, the comparator1042, the demagnetization detection component 1044, the leading-edgeblanking component 1050, the flip-flop component 1054, the clockgenerator 1056, the driver component 1058, the sampling-and-holdingcomponents 1062 and 1064, the voltage-to-current converters 1060, 1066and 1068, the switch 1080, the signal amplifier 1086, thevoltage-to-current converter 1088, the switch 1082, and the multipliercomponent 1096 are located on a chip 1010. In yet another example, thecapacitor 1090 is located off the chip 1010. In yet another example, thechip 1010 includes terminals 1012, 1014, 1016, 1017, 1018, and 1019.

According to one embodiment, in CCM, the next switching cycle startsbefore the demagnetization process is completed. For example, the actuallength of the demagnetization process (e.g., T_(demag)) before the nextswitching cycle starts is limited to the off-time of the switch 5020(e.g., T_(off)); hence T_(off) can be represented by T_(demag) in CCM.According to another embodiment, in DCM, the off-time of the switch 5020(e.g., T_(off)) is much longer than the demagnetization period (e.g.,T_(demag)). According to yet another embodiment, in CRM, the off-time ofthe switch 5020 (e.g., T_(off)) is slightly longer than thedemagnetization period (e.g., T_(demag)).

As shown in FIG. 10, the lighting system 1000 receives an input voltage1032 and provides a rectified voltage 1093 and a lamp current 1092(e.g., an output current) to drive one or more LEDs 5090. In oneembodiment, a current that flows through the inductor 5040 is sensed bythe resistor 5060. For example, the resistor 5060 generates, through theterminal 1014 and with the leading-edge blanking component 1050, acurrent sensing signal 1052.

In another embodiment, the sampling-and-holding component 1062 receivesat least a drive signal 1059 and a control signal 1061. For example, thecontrol signal 1061 includes, for each switching cycle, a pulse that hasa rising edge at the beginning of the on-time of the switch 5020 (e.g.,at the rising edge of the drive signal 1059). In another example, duringthe pulse, the current sensing signal 1052 (e.g., V_(cs)) is sampled andheld as a voltage signal 1063 (e.g., V_(s2)). In yet another example,after the falling edge of the pulse, the voltage signal 1063 remainsconstant (e.g., being equal to V_(cs) _(_) ₀) until the next pulse ofthe control signal 1061. In one embodiment, the pulse of the controlsignal 1061 is so narrow that V_(cs) _(_) ₀ equals approximately andthus represents the current sensing signal 1052 at the beginning of theon-time of the switch 5020.

In yet another embodiment, the sampling-and-holding component 1064receives at least the drive signal 1059, which includes, for eachswitching cycle, a pulse that has a width corresponding to the on-timeof the switch 5020 (e.g., T_(on)). For example, during the pulse of thedrive signal 1059, the current sensing signal 1052 (e.g., V_(cs)) issampled and held as a voltage signal 1065 (e.g., V_(s3)). In anotherexample, after the falling edge of the pulse, the voltage signal 1065remains constant (e.g., being equal to V_(cs) _(_) _(p)) until the nextpulse of the drive signal 1059.

As shown in FIG. 10, the voltage signals 1063 and 1065 are received bythe voltage-to-current converters 1066 and 1068, which in responsegenerate current signals 1067 and 1069, respectively, according to oneembodiment. For example, the current signal 1067 is represented byI_(s2), and the current signal 1069 is represented by I_(s3). In anotherexample, the sum of the current signals 1067 and 1069 forms a sinkingcurrent 1081 (e.g., I_(sink2)), which is used to discharge the capacitor1090 if the switch 1080 is closed.

According to another embodiment, the switch 1080 is controlled by aDemag signal 1045, which is generated by the demagnetization detectioncomponent 1044. For example, if the Demag signal 1045 is at the logichigh level, the switch 1080 is closed. In another example, the switch1080 is closed during the demagnetization period and is open during therest of the switching period. In yet another example, the sinkingcurrent 1081 discharges the capacitor 1090 during the demagnetizationperiod (e.g., during T_(demag)).

Also, as shown in FIG. 10, the signal amplifier 1086 receives thecurrent sensing signal 1052 (e.g., V_(cs)) and generates a voltagesignal 1087 (e.g., V_(s1)) according to one embodiment. For example, thevoltage signal 1087 (e.g., V_(s1)) equals two times the current sensingsignal 1052 (e.g., V_(cs)) in magnitude. According to anotherembodiment, the voltage signal 1087 is received by thevoltage-to-current converter 1088, which in response generates a sinkingcurrent 1089 (e.g., I_(sink1)). For example, the sinking current 1089 isused to discharge the capacitor 1090 if the switch 1082 is closed.

According to yet another embodiment, the switch 1082 is controlled by asignal 1085, which has been generated based on the signal 1059. Forexample, if the signal 1085 is at the logic high level, the switch 1082is closed, and if the signal 1085 is at the logic low level, the switch1082 is open. In another example, the switch 1082 is closed during theon-time of the switch 5020, and is open during the off-time of theswitch 5020. In yet another example, the sinking current 1089 dischargesthe capacitor 1090 during the on-time of the switch 5020. According toyet another embodiment, the voltage-to-current converter 1060 receives apredetermined voltage signal 1091 (e.g., V_(ref)), and in responsegenerates a charging current 1061 (e.g., I_(ref)). For example, thecharging current 1061 charges the capacitor 1090 during the switchingperiod (e.g., during T_(s)). According to yet another embodiment, thesignal 1083 (e.g., V_(C)) is generated by the charging current 1061(e.g., I_(ref)), the discharging current 1081 (e.g., I_(sink2)), and thedischarging current 1089 (e.g., I_(sink1)) for the capacitor 1090. Forexample, the signal 1083 (e.g., V_(C)) decreases in magnitude during thedemagnetization period (e.g., during T_(demag)), and increases duringthe rest of the switching cycle.

As shown in FIG. 10, the resistor 1098 receives the rectified voltage1093, and together with the resistor 1099, generates a signal 1095. Forexample, the signal 1095 is received by the multiplier component 1096through the terminal 1017. In another example, the multiplier component1096 also receives the signal 1083 (e.g., V_(C)) and generates a controlsignal 1097 based on at least information associated with the signals1095 and 1083.

In one embodiment, the comparator 1042 receives the control signal 1097,and also receives the current sensing signal 1052 through the slopecompensation component 1084. For example, in response, the comparator1042 generates a comparison signal 1043, which is received by theflip-flop component 1054. In another example, the flip-flop component1054 also receives a clock signal 1055 from the clock generator 1056 andgenerates a modulation signal 1057. In yet another example, themodulation signal 1057 is received by the driver component 1058, whichin response outputs the drive signal 1059 to the switch 5020 and thesampling-and-holding components 1062 and 1064. In another embodiment,for DCM, CCM and CRM, the lighting system 1000 has power factor that isequal to or larger than 0.9, such as being equal to 1. For example, thehigh power factor and precise control of constant lamp current 1092 aresimultaneously achieved by the lighting system 1000.

In yet another embodiment, if, over a plurality of switching cycles, thecharging and the discharging of the capacitor 1090 are equal, thelighting system 1000 reaches the equilibrium (e.g., the steady state),as follows:

$\begin{matrix}{{\sum\limits_{i = 0}^{N}{I_{ref} \times {T_{s}(i)}}} = {{\sum\limits_{i = 0}^{N}{\frac{1}{2} \times {I_{\sin \; k\; 1\_ \; p}(i)} \times {T_{on}(i)}}} + {{I_{{sink}\; 2}(i)} \times {T_{demag}(i)}}}} & \left( {{Equation}\mspace{14mu} 39} \right)\end{matrix}$

where i represents the ith switching cycle.

As discussed above and further emphasized here, FIG. 10 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the leading-edge blanking component 1050is removed, and the signal 1052 is received directly from the terminal1014. In another example, the capacitor 1090 is located on the chip1010. In yet another example, a low-pass filter and/or a buffer areadded to process the signal 1083 before the signal 1083 is received bythe multiplier component 1096. In yet another example, two resistors arefurther added to divide the processed signal 1083 before the processedsignal 1083 is received by the multiplier component 1096.

In yet another example, for DCM and CRM, V_(cs) _(_) ₀ is equal to zero,so the sampling-and-holding component 1062 and the voltage-to-currentconverter 1066 are removed if the lighting system 1000 does not need tooperate in DCM and CRM for constant lamp current 1092. In yet anotherexample, for CRM, the clock generator 1056 is replaced by a pulse signalgenerator, which receives the Demag signal 1045 and in responsegenerates pulses of a pulse signal 1055. In yet another example, thepulse signal 1055 is received by the flip-flop component 1054, anddifferent pulses of the pulse signal 1055 correspond to differentswitching cycles.

FIG. 11 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention. This diagram is merelyan example, which should not unduly limit the scope of the claims. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications. The lighting system 1100 includes aswitch 5120, a diode 5130, an inductor 5140, capacitors 5150 and 5152,and a sensing resistor 5160. Additionally, the lighting system 1100 alsoincludes a comparator 1142, a demagnetization detection component 1144,a leading-edge blanking component 1150, a flip-flop component 1154, apulse signal generator 1156, and a driver component 1158. Moreover, thelighting system 1100 also includes a transconductance amplifier 1186,switches 1180 and 1182, a capacitor 1190, and a ramping signal generator1199.

For example, the switch 5120, the diode 5130, the inductor 5140, thecapacitor 5150, and the sensing resistor 5160 are the same as the powerswitch 120, the diode 130, the inductor 140, the capacitor 150, and thesensing resistor 160, respectively. In another example, the comparator1142, the demagnetization detection component 1144, the leading-edgeblanking component 1150, the flip-flop component 1154, the pulse signalgenerator 1156, the driver component 1158, the transconductanceamplifier 1186, the switches 1180 and 1182, and the ramping signalgenerator 1199 are located on a chip 1110. In yet another example, thecapacitor 1190 is located off the chip 1110. In yet another example, thechip 1110 includes terminals 1112, 1114, 1116, 1118, and 1119.

As shown in FIG. 11, the lighting system 1100 receives an input voltage1132 and provides a lamp current 1192 (e.g., an output current) and alamp voltage to one or more LEDs 5190. In one embodiment, a current thatflows through the inductor 5140 is sensed by the resistor 5160. Forexample, the resistor 5160 generates, through the terminal 1114 and withthe leading-edge blanking component 1150, a current sensing signal 1152.

In another embodiment, the transconductance amplifier 1186 receives thecurrent sensing signal 1152 (e.g., V_(cs)), and also receives apredetermined voltage signal 1191 (e.g., V_(ref)) through the switch1180. For example, the switch 1180 is controlled by a signal 1185, whichhas been generated based on a drive signal 1159. In another example, ifthe signal 1185 is at the logic high level, the switch 1180 is closed,and if the signal 1185 is at the logic low level, the switch 1180 isopen. In yet another example, the switch 1180 is closed during theon-time of the switch 5120, and is open during the off-time of theswitch 5120.

In yet another embodiment, during the on-time of the switch 5120, thetransconductance amplifier 1186 compares the current sensing signal 1152(e.g., V_(cs)) and the predetermined voltage signal 1191 (e.g.,V_(ref)), and converts the difference between the current sensing signal1152 (e.g., V_(cs)) and the predetermined voltage signal 1191 (e.g.,V_(ref)) into a current 1189. For example, the current 1189 isproportional to the difference between the current sensing signal 1152(e.g., V_(cs)) and the predetermined voltage signal 1191 (e.g.,V_(ref)). In another example, during the on-time of the switch 5120, thecurrent 1189 charges the capacitor 1190 if the predetermined voltagesignal 1191 (e.g., V_(ref)) is larger than the current sensing signal1152 (e.g., V_(cs)) in magnitude, and discharges the capacitor 1190 ifthe predetermined voltage signal 1191 (e.g., V_(ref)) is smaller thanthe current sensing signal 1152 (e.g., V_(cs)) in magnitude.

In yet another embodiment, during the off-time of the switch 5120, thepredetermined voltage signal 1191 (e.g., V_(ref)) is shorted to theground through the switch 1182. For example, the switch 1182 iscontrolled by a signal 1145, which has been generated based on the drivesignal 1159. In another example, if the signal 1145 is at the logic highlevel, the switch 1182 is closed, and if the signal 1145 is at the logiclow level, the switch 1182 is open. In yet another example, the switch1182 is closed during the off-time of the switch 5120, and is openduring the on-time of the switch 5120.

As shown in FIG. 11, a signal 1183 (e.g., V_(C)) is generated by thecurrent 1189 charging and/or discharging the capacitor 1190. In oneembodiment, the comparator 1142 receives the signal 1183 (e.g., V_(C))and also receives a ramping signal 1193. For example, the ramping signal1193 is generated by the ramping signal generator 1199 in response to apulse signal 1155. In another example, in response, the comparator 1142generates a comparison signal 1143, which is received by the flip-flopcomponent 1154. In another example, the flip-flop component 1154 alsoreceives the pulse signal 1155 from the pulse signal generator 1156 andgenerates a modulation signal 1157. In yet another example, themodulation signal 1157 is received by the driver component 1158, whichin response outputs the drive signal 1159 to the switch 5120. In anotherembodiment, the pulse signal generator 1156 receives a Demag signal 1145from the demagnetization detection component 1144, and in responsegenerates pulses of the pulse signal 1155. For example, different pulsesof the pulse signal 1155 correspond to different switching cycles.

As discussed above and further emphasized here, FIG. 11 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the leading-edge blanking component 1150is removed, and the signal 1152 is received directly from the terminal1114. In another example, the capacitor 1190 is located on the chip1110.

FIG. 12 is a simplified diagram for a LED lighting system according toyet another embodiment of the present invention. This diagram is merelyan example, which should not unduly limit the scope of the claims. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications. The lighting system 1200 includes aswitch 5220, a diode 5230, an inductor 5240, capacitors 5250 and 5252,and a sensing resistor 5260. Additionally, the lighting system 1200 alsoincludes a comparator 1242, a demagnetization detection component 1244,a leading-edge blanking component 1250, a flip-flop component 1254, apulse signal generator 1256, and a driver component 1258. Moreover, thelighting system 1200 also includes a transconductance amplifier 1286,switches 1280 and 1282, a capacitor 1290, a multiplier component 1296,and resistors 1298 and 1299.

For example, the switch 5220, the diode 5230, the inductor 5240, thecapacitor 5250, and the sensing resistor 5260 are the same as the powerswitch 120, the diode 130, the inductor 140, the capacitor 150, and thesensing resistor 160, respectively. In another example, the comparator1242, the demagnetization detection component 1244, the leading-edgeblanking component 1250, the flip-flop component 1254, the pulse signalgenerator 1256, the driver component 1258, the transconductanceamplifier 1286, the switches 1280 and 1282, and the multiplier component1296 are located on a chip 1210. In yet another example, the capacitor1290 is located off the chip 1210. In yet another example, the chip 1210includes terminals 1212, 1214, 1216, 1217, 1218, and 1219.

As shown in FIG. 12, the lighting system 1200 receives an input voltage1232 and provides a rectified voltage 1293 and a lamp current 1292(e.g., an output current) to drive one or more LEDs 5290. In oneembodiment, a current that flows through the inductor 5240 is sensed bythe resistor 5260. For example, the resistor 5260 generates, through theterminal 1214 and with the leading-edge blanking component 1250, acurrent sensing signal 1252.

In another embodiment, the transconductance amplifier 1286 receives thecurrent sensing signal 1252 (e.g., V_(cs)), and also receives apredetermined voltage signal 1291 (e.g., V_(ref)) through the switch1280. For example, the switch 1280 is controlled by a signal 1285, whichhas been generated based on a drive signal 1259. In another example, ifthe signal 1285 is at the logic high level, the switch 1280 is closed,and if the signal 1285 is at the logic low level, the switch 1280 isopen. In yet another example, the switch 1280 is closed during theon-time of the switch 5220, and is open during the off-time of theswitch 5220.

In yet another embodiment, during the on-time of the switch 5220, thetransconductance amplifier 1286 compares the current sensing signal 1252(e.g., V_(cs)) and the predetermined voltage signal 1291 (e.g.,V_(ref)), and converts the difference between the current sensing signal1252 (e.g., V_(cs)) and the predetermined voltage signal 1291 (e.g.,V_(ref)) into a current 1289. For example, the current 1289 isproportional to the difference between the current sensing signal 1252(e.g., V_(cs)) and the predetermined voltage signal 1291 (e.g.,V_(ref)). In another example, during the on-time of the switch 5220, thecurrent 1289 charges the capacitor 1290 if the predetermined voltagesignal 1291 (e.g., V_(ref)) is larger than the current sensing signal1252 (e.g., V_(cs)) in magnitude, and discharges the capacitor 1290 ifthe predetermined voltage signal 1291 (e.g., V_(ref)) is smaller thanthe current sensing signal 1252 (e.g., V_(cs)) in magnitude.

In yet another embodiment, during the off-time of the switch 5220, thepredetermined voltage signal 1291 (e.g., V_(ref)) is shorted to theground through the switch 1282. For example, the switch 1282 iscontrolled by a signal 1245, which has been generated based on the drivesignal 1259. In another example, if the signal 1245 is at the logic highlevel, the switch 1282 is closed, and if the signal 1245 is at the logiclow level, the switch 1282 is open. In yet another example, the switch1282 is closed during the off-time of the switch 5220, and is openduring the on-time of the switch 5220.

As shown in FIG. 12, a signal 1283 (e.g., V_(C)) is generated by thecurrent 1289 charging and/or discharging the capacitor 1290. In oneembodiment, the resistor 1298 receives the rectified voltage 1293, andtogether with the resistor 1299, generates a signal 1295. For example,the signal 1295 is received by the multiplier component 1296 through theterminal 1217. In another example, the multiplier component 1296 alsoreceives the signal 1283 (e.g., V_(C)) and generates a control signal1297 based on at least information associated with the signals 1295 and1283.

In another embodiment, the comparator 1242 receives the control signal1297, and also receives the current sensing signal 1252. For example, inresponse, the comparator 1242 generates a comparison signal 1243, whichis received by the flip-flop component 1254. In another example, theflip-flop component 1254 also receives a pulse signal 1255 from thepulse signal generator 1256 and generates a modulation signal 1257. Inyet another example, the modulation signal 1257 is received by thedriver component 1258, which in response outputs the drive signal 1259to the switch 5220. In yet another embodiment, the pulse signalgenerator 1256 receives a Demag signal 1245 from the demagnetizationdetection component 1244, and in response generates pulses of the pulsesignal 1255. For example, different pulses of the pulse signal 1255correspond to different switching cycles.

As discussed above and further emphasized here, FIG. 12 is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, the leading-edge blanking component 1250is removed, and the signal 1252 is received directly from the terminal1214. In another example, the capacitor 1290 is located on the chip1210. In yet another example, a slope compensation component is added,through which the comparator 1242 receives the current sensing signal1252.

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined. In yet another example, various embodiments and/orexamples of the present invention are combined so that a lighting systemcan provide constant lamp current in various operation modes, such as inall of the DCM mode, the CCM mode and the CRM mode under certainconditions (e.g., with different input voltages).

The present invention has a wide range of applications. Certainembodiments of the present invention can be used to drive one or morelight emitting diodes with high power factor and precise control ofconstant lamp current.

According to another embodiment, a system (e.g., as implementedaccording to FIG. 3) for providing at least an output current to one ormore light emitting diodes includes a control component (e.g., thecomponent 380) configured to receive at least a demagnetization signal(e.g., the signal 383), a sensed signal (e.g., the signal 314) and areference signal (e.g., the signal 389) and to generate a control signal(e.g., the signal 391) based on at least information associated with thedemagnetization signal, the sensed signal and the reference signal, anda logic and driving component (e.g., the components 362, 394 and 396)configured to receive at least the control signal (e.g., the signal 391)and output a drive signal (e.g., the signal 312) to a switch (e.g., thecomponent 320) based on at least information associated with the controlsignal (e.g., the signal 391). The switch (e.g., the component 320) isconnected to a first diode terminal of a diode (e.g., the component 330)and a first inductor terminal of an inductor (e.g., the component 340).The diode further includes a second diode terminal, and the inductorfurther includes a second inductor terminal. The second diode terminaland the second inductor terminal are configured to provide at least theoutput current to the one or more light emitting diodes. The controlsignal (e.g., the signal 391) is configured to regulate the outputcurrent at a constant magnitude.

According to yet another embodiment, a method (e.g., as implementedaccording to FIG. 3) for providing at least an output current to one ormore light emitting diodes includes receiving at least a demagnetizationsignal (e.g., the signal 383), a sensed signal (e.g., the signal 314)and a reference signal (e.g., the signal 389), processing informationassociated with the demagnetization signal, the sensed signal and thereference signal, and generating a control signal (e.g., the signal 391)based on at least information associated with the demagnetizationsignal, the sensed signal and the reference signal. Additionally, themethod includes receiving at least the control signal (e.g., the signal391), processing information associated with the control signal, andoutputting a drive signal (e.g., the signal 312) to a switch (e.g., thecomponent 320) connected to a first diode terminal of a diode (e.g., thecomponent 330) and a first inductor terminal of an inductor (e.g., thecomponent 340). The diode further includes a second diode terminal, andthe inductor further includes a second inductor terminal. The seconddiode terminal and the second inductor terminal are configured toprovide at least the output current to the one or more light emittingdiodes. Moreover, the method includes regulating the output current at apredetermined magnitude based on at least information associated withthe control signal (e.g., the signal 391).

According to yet another embodiment, a system (e.g., as implementedaccording to FIG. 5) for providing at least an output current to one ormore light emitting diodes includes a first signal processing component(e.g., the component 520) configured to receive at least a sensed signal(e.g., the signal 552) and generate a first signal (e.g., the signal521). The sensed signal is associated with an inductor current flowingthrough an inductor coupled to a switch. Additionally, the systemincludes a second signal processing component (e.g., the component 522)configured to generate a second signal (e.g., the signal 523), anintegrator component (e.g., the components 530 and 540) configured toreceive the first signal and the second signal and generate a thirdsignal (e.g., the signal 531), and a comparator (e.g., the component542) configured to process information associated with the third signaland the sensed signal and generate a comparison signal (e.g., the signal543) based on at least information associated with the third signal andthe sensed signal. Moreover, the system includes a signal generator(e.g., the component 554) configured to receive at least the comparisonsignal and generate a modulation signal (e.g., the signal 557), and agate driver (e.g., the component 558) configured to receive themodulation signal (e.g., the signal 557) and output a drive signal tothe switch. The drive signal is associated with at least one or moreswitching periods, and each of the one or more switching periodsincludes at least an on-time period for the switch and a demagnetizationperiod for a demagnetization process. For each of the one or moreswitching periods, the first signal represents a multiplication resultof a first sum of the on-time period and the demagnetization period anda second sum of a first current magnitude and a second currentmagnitude, and the second signal represents the switching periodmultiplied by a predetermined current magnitude. The first currentmagnitude represents the inductor current at the beginning of theon-time period, and the second current magnitude represents the inductorcurrent at the end of the on-time period. The integrator component isfurther configured to integrate period-by-period differences between thefirst signal and the second signal for a plurality of switching periods,and the third signal (e.g., the signal 531) represents the integratedperiod-by-period differences. The integrated period-by-perioddifferences are smaller than a predetermined threshold in magnitude.

According to yet another embodiment, a method (e.g., as implementedaccording to FIG. 5) for providing at least an output current to one ormore light emitting diodes includes receiving at least a sensed signal.The sensed signal is associated with an inductor current flowing throughan inductor coupled to a switch. Additionally, the method includesprocessing information associated with the sensed signal, generating afirst signal based on at least information associated with the sensedsignal, generating a second signal, receiving the first signal and thesecond signal, processing information associated with the first signaland the second signal, and generating a third signal based on at leastinformation associated with the first signal and the second signal.Moreover, the method includes processing information associated with thethird signal and the sensed signal, generating a comparison signal basedon at least information associated with the third signal and the sensedsignal, receiving at least the comparison signal, generating amodulation signal based on at least information associated with thecomparison signal, receiving the modulation signal, and outputting adrive signal based on at least information associated with themodulation signal. The drive signal is associated with at least one ormore switching periods, and each of the one or more switching periodsincludes at least an on-time period and a demagnetization period. Foreach of the one or more switching periods, the first signal represents amultiplication result of a first sum of the on-time period and thedemagnetization period and a second sum of a first current magnitude anda second current magnitude, and the second signal represents theswitching period multiplied by a predetermined current magnitude. Thefirst current magnitude represents the inductor current at the beginningof the on-time period, and the second current magnitude represents theinductor current at the end of the on-time period. The process forprocessing information associated with the first signal and the secondsignal includes integrating period-by-period differences between thefirst signal and the second signal for a plurality of switching periods,and the third signal represents the integrated period-by-perioddifferences. The integrated period-by-period differences are smallerthan a predetermined threshold in magnitude.

According to yet another embodiment, a system (e.g., as implementedaccording to FIG. 5) for providing at least an output current to one ormore light emitting diodes includes a first signal processing component(e.g., the component 520) configured to receive at least a sensed signal(e.g., the signal 552) and generate a first signal (e.g., the signal521). The sensed signal is associated with an inductor current flowingthrough an inductor coupled to a switch. Additionally, the systemincludes a second signal processing component (e.g., the component 522)configured to generate a second signal (e.g., the signal 523), anintegrator component (e.g., the components 530 and 540) configured toreceive the first signal and the second signal and generate a thirdsignal (e.g., the signal 531), and a comparator (e.g., the component542) configured to process information associated with the third signaland the sensed signal and generate a comparison signal (e.g., the signal543) based on at least information associated with the third signal andthe sensed signal. Moreover, the system includes a signal generator(e.g., the component 554) configured to receive at least the comparisonsignal and generate a modulation signal (e.g., the signal 557), and agate driver (e.g., the component 558) configured to receive themodulation signal (e.g., the signal 557) and output a drive signal tothe switch. The drive signal is associated with at least one or moreswitching periods, and each of the one or more switching periodsincludes at least an on-time period for the switch and a demagnetizationperiod for a demagnetization process. For each of the one or moreswitching periods, the first signal represents a sum of a firstmultiplication result and a second multiplication result, and the secondsignal represents the switching period multiplied by a predeterminedcurrent magnitude. The first multiplication result is equal to theon-time period multiplied by a sum of a first current magnitude and asecond current magnitude. The first current magnitude represents theinductor current at the beginning of the on-time period, and the secondcurrent magnitude represents the inductor current at the end of theon-time period. The second multiplication result is equal to twomultiplied by the demagnetization period and further multiplied by athird current magnitude, and the third current magnitude represents theinductor current at the middle of the on-time period. The integratorcomponent is further configured to integrate period-by-perioddifferences between the first signal and the second signal for aplurality of switching periods, and the third signal (e.g., the signal531) represents the integrated period-by-period differences. Theintegrated period-by-period differences are smaller than a predeterminedthreshold in magnitude.

According to yet another embodiment, a method (e.g., as implementedaccording to FIG. 5) for providing at least an output current to one ormore light emitting diodes includes receiving at least a sensed signal.The sensed signal is associated with an inductor current flowing throughan inductor coupled to a switch. Additionally, the method includesprocessing information associated with the sensed signal, generating afirst signal based on at least information associated with the sensedsignal, generating a second signal, receiving the first signal and thesecond signal, processing information associated with the first signaland the second signal, and generating a third signal based on at leastinformation associated with the first signal and the second signal.Moreover, the method includes processing information associated with thethird signal and the sensed signal, generating a comparison signal basedon at least information associated with the third signal and the sensedsignal, receiving at least the comparison signal, and generating amodulation signal based on at least information associated with thecomparison signal. Also, the method includes receiving the modulationsignal, and outputting a drive signal based on at least informationassociated with the modulation signal. The drive signal is associatedwith at least one or more switching periods, and each of the one or moreswitching periods includes at least an on-time period and ademagnetization period. For each of the one or more switching periods,the first signal represents a sum of a first multiplication result and asecond multiplication result, and the second signal represents theswitching period multiplied by a predetermined current magnitude. Thefirst multiplication result is equal to the on-time period multiplied bya sum of a first current magnitude and a second current magnitude. Thefirst current magnitude represents the inductor current at the beginningof the on-time period, and the second current magnitude represents theinductor current at the end of the on-time period. The secondmultiplication result is equal to two multiplied by the demagnetizationperiod and further multiplied by a third current magnitude, and thethird current magnitude represents the inductor current at the middle ofthe on-time period. The process for processing information associatedwith the first signal and the second signal includes integratingperiod-by-period differences between the first signal and the secondsignal for a plurality of switching periods, and the third signalrepresents the integrated period-by-period differences. The integratedperiod-by-period differences are smaller than a predetermined thresholdin magnitude.

According to yet another embodiment, a system (e.g., as implementedaccording to FIG. 6) for providing at least an output current to one ormore light emitting diodes includes a first sampling-and-holding andvoltage-to-current-conversion component (e.g., the components 662 and666) configured to receive at least a sensed signal and generate a firstcurrent signal (e.g., the signal 667). The sensed signal is associatedwith an inductor current flowing through an inductor coupled to a firstswitch. Additionally, the system includes a second sampling-and-holdingand voltage-to-current-conversion component (e.g., the components 664and 668) configured to receive at least the sensed signal and generate asecond current signal (e.g., the signal 669), and a signal-amplificationand voltage-to-current-conversion component (e.g., the components 686and 688) configured to receive at least the sensed signal and generate athird current signal (e.g., the signal 689). Moreover, the systemincludes a current-signal generator configured to generate a fourthcurrent signal (e.g., the signal 661), and a capacitor coupled to thecurrent-signal generator, coupled through a second switch to the firstsampling-and-holding and voltage-to-current-conversion component and thesecond sampling-and-holding and voltage-to-current-conversion component,and coupled through a third switch to the signal-amplification andvoltage-to-current-conversion component. The capacitor is configured togenerate a voltage signal. Also, the system includes a comparator (e.g.,the component 642) configured to process information associated with thevoltage signal (e.g., the signal 683) and the sensed signal (e.g., thesignal 652) and generate a comparison signal (e.g., the signal 643)based on at least information associated with the voltage signal and thesensed signal. Additionally, the system includes a modulation-signalgenerator (e.g., the component 654) configured to receive at least thecomparison signal and generate a modulation signal (e.g., the signal657), and a gate driver configured to receive the modulation signal andoutput a drive signal to the first switch. The drive signal isassociated with at least one or more switching periods, and each of theone or more switching periods includes at least an on-time period forthe first switch and a demagnetization period for a demagnetizationprocess. The first current signal represents the inductor current at thebeginning of the on-time period, the second current signal representsthe inductor current at the end of the on-time period, and the thirdcurrent signal represents the inductor current. For each of the one ormore switching periods, the first current signal and the second currentsignal are configured to discharge or charge the capacitor during onlythe demagnetization period, the third current signal is configured todischarge or charge the capacitor during only the on-time period, andthe fourth current signal is configured to charge or discharge thecapacitor during the switching period.

According to yet another embodiment, a method (e.g., as implementedaccording to FIG. 6) for providing at least an output current to one ormore light emitting diodes includes receiving at least a sensed signal.The sensed signal is associated with an inductor current flowing throughan inductor coupled to a switch, processing information associated withthe sensed signal, and generating a first current signal, a secondcurrent signal, and a third current signal based on at least informationassociated with the sensed signal. Additionally, the method includesgenerating a fourth current signal, processing information associatedwith the first current signal, the second current signal, the thirdcurrent signal, and the fourth current signal, and generating a voltagesignal, by at least a capacitor, based on at least informationassociated with the first current signal, the second current signal, thethird current signal, and the fourth current signal. Moreover, themethod includes processing information associated with the voltagesignal and the sensed signal, generating a comparison signal based on atleast information associated with the voltage signal and the sensedsignal, receiving at least the comparison signal, and generating amodulation signal based on at least information associated with thecomparison signal. Also, the method includes receiving the modulationsignal, and outputting a drive signal based on at least informationassociated with the modulation signal. The drive signal is associatedwith at least one or more switching periods, and each of the one or moreswitching periods includes at least an on-time period and ademagnetization period. The first current signal represents the inductorcurrent at the beginning of the on-time period, the second currentsignal represents the inductor current at the end of the on-time period,and the third current signal represents the inductor current. For eachof the one or more switching periods, the process for processinginformation associated with the first current signal, the second currentsignal, the third current signal, and the fourth current signal includesdischarging or charging the capacitor with the first current signal andthe second current signal during only the demagnetization period,discharging or charging the capacitor with the third current signalduring only the on-time period, and charging or discharging thecapacitor with the fourth current signal during the switching period.

According to yet another embodiment, a system (e.g., as implementedaccording to FIG. 7) for providing at least an output current to one ormore light emitting diodes includes a signal-amplification andvoltage-to-current-conversion component (e.g., the components 786 and788) configured to receive at least a sensed signal (e.g., the signal752) and generate a first current signal (e.g., the signal 789). Thesensed signal is associated with an inductor current flowing through aninductor coupled to a first switch. Additionally, the system includes acurrent-signal generator configured to generate a second current signal(e.g., the signal 761), and a capacitor coupled to the current-signalgenerator, and coupled through a second switch to thesignal-amplification and voltage-to-current-conversion component. Thecapacitor is configured to generate a voltage signal. Moreover, thesystem includes a comparator configured to process informationassociated with the voltage signal and the sensed signal and generate acomparison signal based on at least information associated with thevoltage signal and the sensed signal, a modulation-signal generator(e.g., the component 754) configured to receive at least the comparisonsignal and generate a modulation signal (e.g., the signal 757), and agate driver configured to receive the modulation signal and output adrive signal to the first switch. The drive signal is associated with atleast one or more switching periods, and the first current signalrepresents the inductor current. Each of the one or more switchingperiods includes at least an on-time period for the first switch. Foreach of the one or more switching periods, the first current signal isconfigured to discharge or charge the capacitor during only the on-timeperiod, and the second current signal is configured to charge ordischarge the capacitor during only the on-time period.

According to yet another embodiment, a method (e.g., as implementedaccording to FIG. 7) for providing at least an output current to one ormore light emitting diodes includes receiving at least a sensed signal.The sensed signal is associated with an inductor current flowing throughan inductor coupled to a switch. Additionally, the method includesprocessing information associated with the sensed signal, generating afirst current signal based on at least information associated with thesensed signal, generating a second current signal, processinginformation associated with the first current signal and the secondcurrent signal, and generating a voltage signal, by at least acapacitor, based on at least information associated with the firstcurrent signal and the second current signal. Moreover, the methodincludes processing information associated with the voltage signal andthe sensed signal, generating a comparison signal (e.g., the signal 743)based on at least information associated with the voltage signal and thesensed signal, receiving at least the comparison signal, generating amodulation signal based on at least information associated with thecomparison signal, receiving the modulation signal, and outputting adrive signal based on at least information associated with themodulation signal. The drive signal is associated with at least one ormore switching periods, and the first current signal represents theinductor current. Each of the one or more switching periods includes atleast an on-time period. For each of the one or more switching periods,the process for processing information associated with the first currentsignal and the second current signal includes discharging or chargingthe capacitor with the first current signal during only the on-timeperiod, and charging or discharging the capacitor with the secondcurrent signal during only the on-time period.

According to yet another embodiment, a system (e.g., as implementedaccording to FIG. 8 and/or FIG. 9) for providing at least an outputcurrent to one or more light emitting diodes includes a transconductanceamplifier (e.g., the component 886 and/or the component 986) configuredto receive a sensed signal and also receive a predetermined voltagesignal (e.g., the signal 891 and/or the signal 991) through a firstswitch (e.g., the component 880 and/or the component 980). The sensedsignal is associated with an inductor current flowing through aninductor coupled to a second switch (e.g., the component 4820 and/or thecomponent 4920), and the transconductance amplifier is furtherconfigured to generate a current signal (e.g., the signal 889 and/or thesignal 989). Additionally, the system includes a capacitor coupled tothe transconductance amplifier and configured to generate a voltagesignal (e.g., the signal 883 and/or the signal 983), and a comparatorconfigured to process information associated with the voltage signal andthe sensed signal and generate a comparison signal (e.g., the signal 843and/or the signal 943) based on at least information associated with thevoltage signal and the sensed signal. Moreover, the system includes amodulation-signal generator (e.g., the component 854 and/or thecomponent 954) configured to receive at least the comparison signal andgenerate a modulation signal (e.g., the signal 857 and/or the signal957), and a gate driver configured to receive the modulation signal andoutput a drive signal to the second switch. The drive signal isassociated with at least one or more switching periods, and each of theone or more switching periods includes at least an on-time period forthe second switch. The transconductance amplifier (e.g., the component886 and/or the component 986) is further configured to, for each of theone or more switching periods, receive at least a predetermined voltagesignal only during the on-time period. The current signal (e.g., thesignal 889 and/or the signal 989) is configured to charge or dischargethe capacitor.

According to yet another embodiment, a method (e.g., as implementedaccording to FIG. 8 and/or FIG. 9) for providing at least an outputcurrent to one or more light emitting diodes includes receiving at leasta sensed signal. The sensed signal is associated with an inductorcurrent flowing through an inductor coupled to a switch. Additionally,the method includes processing information associated with the sensedsignal and a predetermined voltage signal (e.g., the signal 891 and/orthe signal 991), generating a current signal based on at leastinformation associated with the sensed signal and the predeterminedvoltage signal, and processing information associated with the currentsignal. Moreover, the method includes generating a voltage signal, by atleast a capacitor, based on at least information associated with thecurrent signal, processing information associated with the voltagesignal and the sensed signal, and generating a comparison signal basedon at least information associated with the voltage signal and thesensed signal. Also, the method includes receiving at least thecomparison signal, generating a modulation signal based on at leastinformation associated with the comparison signal, receiving themodulation signal, and outputting a drive signal based on at leastinformation associated with the modulation signal. The drive signal isassociated with at least one or more switching periods, and each of theone or more switching periods includes at least an on-time period. Theprocess for receiving at least a sensed signal includes, for each of theone or more switching periods, receiving at least the predeterminedvoltage signal during only the on-time period. Also, the process forprocessing information associated with the current signal includescharging or discharging the capacitor with the current signal (e.g., thesignal 889 and/or the signal 989).

According to yet another embodiment, a system (e.g., as implementedaccording to FIG. 10) for providing at least an output current to one ormore light emitting diodes includes a first sampling-and-holding andvoltage-to-current-conversion component (e.g., the components 1062 and1066) configured to receive at least a sensed signal and generate afirst current signal (e.g., the signal 1067). The sensed signal isassociated with an inductor current flowing through an inductor coupledto a first switch. Additionally, the system includes a secondsampling-and-holding and voltage-to-current-conversion component (e.g.,the components 1064 and 1068) configured to receive at least the sensedsignal and generate a second current signal (e.g., the signal 1069), anda signal-amplification and voltage-to-current-conversion component(e.g., the components 1086 and 1088) configured to receive at least thesensed signal and generate a third current signal (e.g., the signal1089), a current-signal generator configured to generate a fourthcurrent signal (e.g., the signal 1061), and a capacitor coupled to thecurrent-signal generator, coupled through a second switch to the firstsampling-and-holding and voltage-to-current-conversion component and thesecond sampling-and-holding and voltage-to-current-conversion component,and coupled through a third switch to the signal-amplification andvoltage-to-current-conversion component, the capacitor being configuredto generate a first voltage signal (e.g., the signal 1083). Moreover,the system includes a multiplier component (e.g., the component 1096)configured to process information associated with the first voltagesignal (e.g., the signal 1083) and a second voltage signal (e.g., thesignal 1093) and generate a multiplication signal based on at leastinformation associated with the first voltage signal and the secondvoltage signal. Also, the system includes a comparator (e.g., thecomponent 1042) configured to receive the multiplication signal and thesensed signal and generate a comparison signal (e.g., the signal 1043)based on at least information associated with the multiplication signaland the sensed signal, a modulation-signal generator (e.g., thecomponent 1054) configured to receive at least the comparison signal andgenerate a modulation signal (e.g., the signal 1057), and a gate driverconfigured to receive the modulation signal and output a drive signal tothe first switch. The drive signal is associated with at least aplurality of switching periods, and each of the one or more switchingperiods includes at least an on-time period for the first switch and ademagnetization period for a demagnetization process. The first currentsignal represents the inductor current at the beginning of the on-timeperiod, the second current signal represents the inductor current at theend of the on-time period, and the third current signal represents theinductor current. For the plurality of switching periods, the firstcurrent signal and the second current signal are configured to dischargeor charge the capacitor during only the demagnetization period, thethird current signal is configured to discharge or charge the capacitorduring only the on-time period, and the fourth current signal isconfigured to charge or discharge the capacitor during the switchingperiod.

According to yet another embodiment, a method (e.g., as implementedaccording to FIG. 10) for providing at least an output current to one ormore light emitting diodes includes receiving at least a sensed signal.The sensed signal is associated with an inductor current flowing throughan inductor coupled to a switch. Additionally, the method includesprocessing information associated with the sensed signal, and generatinga first current signal, a second current signal, and a third currentsignal based on at least information associated with the sensed signal.Moreover, the method includes generating a fourth current signal,processing information associated with the first current signal, thesecond current signal, the third current signal, and the fourth currentsignal, and generating a first voltage signal, by at least a capacitor,based on at least information associated with the first current signal,the second current signal, the third current signal, and the fourthcurrent signal. Also, the method includes processing informationassociated with the first voltage signal and a second voltage signal,generating a multiplication signal based on at least informationassociated with the first voltage signal and the second voltage signal,receiving the multiplication signal and the sensed signal, andgenerating a comparison signal based on at least information associatedwith the multiplication signal and the sensed signal. Additionally, themethod includes receiving at least the comparison signal, generating amodulation signal based on at least information associated with thecomparison signal, receiving the modulation signal, and outputting adrive signal based on at least information associated with themodulation signal. The drive signal is associated with at least aplurality of switching periods, and each of the plurality of switchingperiods includes at least an on-time period and a demagnetizationperiod. The first current signal represents the inductor current at thebeginning of the on-time period, the second current signal representsthe inductor current at the end of the on-time period, and the thirdcurrent signal represents the inductor current. For each of theplurality of switching periods, the process for processing informationassociated with the first current signal, the second current signal, thethird current signal, and the fourth current signal includes dischargingor charging the capacitor with the first current signal and the secondcurrent signal during only the demagnetization period, discharging orcharging the capacitor with the third current signal during only theon-time period, and charging or discharging the capacitor with thefourth current signal during the switching period.

According to yet another embodiment, a system (e.g., as implementedaccording to FIG. 11) for providing at least an output current to one ormore light emitting diodes includes a transconductance amplifier (e.g.,the component 1186) configured to receive a sensed signal and alsoreceive a predetermined voltage signal (e.g., the signal 1191) through afirst switch (e.g., the component 1180). The sensed signal is associatedwith an inductor current flowing through an inductor coupled to a secondswitch (e.g., the component 5120), and the transconductance amplifier(e.g., the component 1186) is further configured to generate a currentsignal (e.g., the signal 1189). Additionally, the system includes acapacitor (e.g., the component 1190) coupled to the transconductanceamplifier and configured to generate a voltage signal (e.g., the signal1183), and a comparator configured to process information associatedwith the voltage signal (e.g., the signal 1183) and a ramping signal(e.g., the signal 1193) and generate a comparison signal (e.g., thesignal 1143) based on at least information associated with the voltagesignal and the ramping signal. Moreover, the system includes amodulation-signal generator (e.g., the component 1154) configured toreceive at least the comparison signal and generate a modulation signal(e.g., the signal 1157), and a gate driver configured to receive themodulation signal and output a drive signal to the second switch. Thedrive signal is associated with at least one or more switching periods,each of the one or more switching periods including at least an on-timeperiod for the second switch. The transconductance amplifier (e.g., thecomponent 1186) is further configured to, for each of the one or moreswitching periods, receive at least a predetermined voltage signal onlyduring the on-time period. The current signal (e.g., the signal 1189) isconfigured to charge or discharge the capacitor.

According to yet another embodiment, a method (e.g., as implementedaccording to FIG. 11) for providing at least an output current to one ormore light emitting diodes includes receiving at least a sensed signal.The sensed signal is associated with an inductor current flowing throughan inductor coupled to a switch. Additionally, the method includesprocessing information associated with the sensed signal and apredetermined voltage signal (e.g., the signal 1191), generating acurrent signal based on at least information associated with the sensedsignal and the predetermined voltage signal, processing informationassociated with the current signal, and generating a voltage signal, byat least a capacitor, based on at least information associated with thecurrent signal. Moreover, the method includes processing informationassociated with the voltage signal and a ramping signal (e.g., thesignal 1193), generating a comparison signal (e.g., the signal 1143)based on at least information associated with the voltage signal and theramping signal, receiving at least the comparison signal, and generatinga modulation signal based on at least information associated with thecomparison signal. Also, the method includes receiving the modulationsignal and outputting a drive signal based on at least informationassociated with the modulation signal. The drive signal is associatedwith at least one or more switching periods, and each of the one or moreswitching periods includes at least an on-time period. The process forreceiving at least a sensed signal includes, for each of the one or moreswitching periods, receiving at least a predetermined voltage signalonly during the on-time period, and the process for processinginformation associated with the current signal includes charging ordischarging the capacitor with the current signal (e.g., the signal1189).

According to yet another embodiment, a system (e.g., as implementedaccording to FIG. 12) for providing at least an output current to one ormore light emitting diodes includes a transconductance amplifier (e.g.,the component 1286) configured to receive a sensed signal and alsoreceive a predetermined voltage signal (e.g., the signal 1291) through afirst switch (e.g., the component 1280). The sensed signal is associatedwith an inductor current flowing through an inductor coupled to a secondswitch, and the transconductance amplifier (e.g., the component 1286) isfurther configured to generate a current signal (e.g., the signal 1289).Additionally, the system includes a capacitor coupled to thetransconductance amplifier and configured to generate a first voltagesignal (e.g., the signal 1283), and a multiplier component (e.g., thecomponent 1296) configured to process information associated with thefirst voltage signal and a second voltage signal and generate amultiplication signal based on at least information associated with thefirst voltage signal and the second voltage signal. Moreover, the systemincludes a comparator (e.g., the component 1242) configured to receivethe multiplication signal and the sensed signal and generate acomparison signal based on at least information associated with themultiplication signal and the sensed signal, a modulation-signalgenerator (e.g., the component 1254) configured to receive at least thecomparison signal and generate a modulation signal (e.g., the signal1257), and a gate driver configured to receive the modulation signal andoutput a drive signal to the second switch. The drive signal isassociated with at least one or more switching periods, each of the oneor more switching periods including at least an on-time period for thesecond switch. The transconductance amplifier (e.g., the component 1286)is further configured to, for each of the one or more switching periods,receive at least a predetermined voltage signal during only the on-timeperiod. The current signal (e.g., the signal 1289) is configured tocharge or discharge the capacitor.

According to yet another embodiment, a method (e.g., as implementedaccording to FIG. 12) for providing at least an output current to one ormore light emitting diodes includes receiving at least a sensed signal.The sensed signal is associated with an inductor current flowing throughan inductor coupled to a switch. Additionally, the method includesprocessing information associated with the sensed signal and apredetermined voltage signal (e.g., the signal 1291), generating acurrent signal based on at least information associated with the sensedsignal and the predetermined voltage signal, processing informationassociated with the current signal, and generating a first voltagesignal (e.g., the signal 1283), by at least a capacitor, based on atleast information associated with the current signal. Moreover, themethod includes processing information associated with the first voltagesignal and a second voltage signal (e.g., the signal 1293), generating amultiplication signal based on at least information associated with thefirst voltage signal and the second voltage signal, receiving themultiplication signal and the sensed signal, and generating a comparisonsignal based on at least information associated with the multiplicationsignal and the sensed signal. Also, the method includes receiving atleast the comparison signal, generating a modulation signal based on atleast information associated with the comparison signal, receiving themodulation signal, and outputting a drive signal based on at leastinformation associated with the modulation signal. The drive signal isassociated with at least one or more switching periods, and each of theone or more switching periods includes at least an on-time period. Theprocess for receiving at least a sensed signal includes, for each of theone or more switching periods, receiving at least a predeterminedvoltage signal during only the on-time period, and the process forprocessing information associated with the current signal includescharging or discharging the capacitor with the current signal (e.g., thesignal 1289).

According to yet another embodiment, a system (e.g., as implementedaccording to FIG. 5) for providing at least an output current to one ormore light emitting diodes includes a first signal processing componentconfigured to receive at least a sensed signal and generate a firstsignal. The sensed signal is associated with an inductor current flowingthrough an inductor coupled to a switch. Additionally, the systemincludes a second signal processing component configured to generate asecond signal, an integrator component configured to receive the firstsignal and the second signal and generate a third signal, a comparatorconfigured to process information associated with the third signal andthe sensed signal and generate a comparison signal based on at leastinformation associated with the third signal and the sensed signal.Moreover, the system includes a signal generator configured to receiveat least the comparison signal and generate a modulation signal, and agate driver configured to receive the modulation signal and output adrive signal to the switch. The drive signal is associated with at leastone or more switching periods, and each of the one or more switchingperiods includes at least an on-time period for the switch and ademagnetization period for a demagnetization process. The first signalprocessing component is further configured to, for each of the one ormore switching periods, sample the sensed signal at the middle of theon-time period, hold the sampled sensed signal representing the inductorcurrent at the middle of the on-time period, and generate the firstsignal representing a sum of a first multiplication result and a secondmultiplication result based on at least information associated with theheld and sampled sensed signal. For each of the one or more switchingperiods, the second signal represents the switching period multiplied bya predetermined current magnitude. The integrator component is furtherconfigured to integrate period-by-period differences between the firstsignal and the second signal for a plurality of switching periods, andthe third signal represents the integrated period-by-period differences.The integrated period-by-period differences are smaller than apredetermined threshold in magnitude.

According to yet another embodiment, a method (e.g., as implementedaccording to FIG. 5) for providing at least an output current to one ormore light emitting diodes includes receiving at least a sensed signal.The sensed signal is associated with an inductor current flowing throughan inductor coupled to a switch. Additionally, the method includesprocessing information associated with the sensed signal, generating afirst signal based on at least information associated with the sensedsignal, generating a second signal, receiving the first signal and thesecond signal, processing information associated with the first signaland the second signal, and generating a third signal based on at leastinformation associated with the first signal and the second signal.Moreover, the method includes processing information associated with thethird signal and the sensed signal, generating a comparison signal basedon at least information associated with the third signal and the sensedsignal, receiving at least the comparison signal, and generating amodulation signal based on at least information associated with thecomparison signal. Also, the method includes receiving the modulationsignal, and outputting a drive signal based on at least informationassociated with the modulation signal. The drive signal is associatedwith at least one or more switching periods, and each of the one or moreswitching periods includes at least an on-time period for the switch anda demagnetization period for a demagnetization process. The process forprocessing information associated with the sensed signal includes, foreach of the one or more switching periods, sampling the sensed signal atthe middle of the on-time period, and holding the sampled sensed signalrepresenting the inductor current at the middle of the on-time period.For each of the one or more switching periods, the first signalrepresents a sum of a first multiplication result and a secondmultiplication result generated based on at least information associatedwith the held and sampled sensed signal, and the second signalrepresents the switching period multiplied by a predetermined currentmagnitude. The process for processing information associated with thefirst signal and the second signal includes integrating period-by-perioddifferences between the first signal and the second signal for aplurality of switching periods, and the third signal represents theintegrated period-by-period differences. The integrated period-by-perioddifferences are smaller than a predetermined threshold in magnitude.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

1.-43. (canceled)
 44. A system for providing at least an output currentto one or more light emitting diodes, the system comprising: a firstsampling-and-holding and voltage-to-current-conversion componentconfigured to receive at least a sensed signal and generate a firstcurrent signal, the sensed signal being associated with an inductorcurrent flowing through an inductor coupled to a first switch; a secondsampling-and-holding and voltage-to-current-conversion componentconfigured to receive at least the sensed signal and generate a secondcurrent signal; a signal-amplification and voltage-to-current-conversioncomponent configured to receive at least the sensed signal and generatea third current signal; a current-signal generator configured togenerate a fourth current signal; a capacitor coupled to thecurrent-signal generator, coupled through a second switch to the firstsampling-and-holding and voltage-to-current-conversion component and thesecond sampling-and-holding and voltage-to-current-conversion component,and coupled through a third switch to the signal-amplification andvoltage-to-current-conversion component, the capacitor being configuredto generate a first voltage signal; a multiplier component configured toprocess information associated with the first voltage signal and asecond voltage signal and generate a multiplication signal based on atleast information associated with the first voltage signal and thesecond voltage signal; a comparator configured to receive themultiplication signal and the sensed signal and generate a comparisonsignal based on at least information associated with the multiplicationsignal and the sensed signal; a modulation-signal generator configuredto receive at least the comparison signal and generate a modulationsignal; and a gate driver configured to receive the modulation signaland output a drive signal to the first switch; wherein: the drive signalis associated with at least a plurality of switching periods, each ofthe one or more switching periods including at least an on-time periodfor the first switch and a demagnetization period for a demagnetizationprocess; the first current signal represents the inductor current at thebeginning of the on-time period; the second current signal representsthe inductor current at the end of the on-time period; and the thirdcurrent signal represents the inductor current; wherein for theplurality of switching periods, the first current signal and the secondcurrent signal are configured to discharge or charge the capacitorduring only the demagnetization period; the third current signal isconfigured to discharge or charge the capacitor during only the on-timeperiod; and the fourth current signal is configured to charge ordischarge the capacitor during the switching period.
 45. The system ofclaim 44 wherein over the plurality of switching periods,accumulatively, one switching period multiplied by the fourth currentsignal is equal to a first sum of a first quantity and a secondquantity, the first quantity being equal to the third current signal atthe end of a corresponding on-time period multiplied by half of thecorresponding on-time period, the second quantity being equal to acorresponding demagnetization period multiplied by a second sum of thefirst current signal and the second current signal in magnitude.
 46. Thesystem of claim 44 wherein the signal-amplification andvoltage-to-current-conversion component includes a signal-amplificationcomponent and a voltage-to-current-conversion component.
 47. The systemof claim 44 wherein: the first sampling-and-holding andvoltage-to-current-conversion component, the second sampling-and-holdingand voltage-to-current-conversion component, the signal-amplificationand voltage-to-current-conversion component, the current-signalgenerator, the multiplier component, the comparator, themodulation-signal generator, and the gate driver are located on a chip;and the capacitor is located off the chip.
 48. The system of claim 44 isconfigured to regulate an output current at a predetermined constantlevel in a discontinuous conduction mode, a continuous conduction mode,and a critical conduction mode.
 49. The system of claim 48 is furtherconfigured to achieve a power factor that is equal to or larger than 0.9in the discontinuous conduction mode, the continuous conduction mode,and the critical conduction mode.
 50. The system of claim 44 isconfigured to regulate an output current at a predetermined constantlevel in a discontinuous conduction mode.
 51. The system of claim 50 isfurther configured to achieve a power factor that is equal to or largerthan 0.9 in the discontinuous conduction mode.
 52. The system of claim44 is configured to regulate an output current at a predeterminedconstant level in a continuous conduction mode.
 53. The system of claim52 is further configured to achieve a power factor that is equal to orlarger than 0.9 in the continuous conduction mode.
 54. The system ofclaim 44 is configured to regulate an output current at a predeterminedconstant level in a critical conduction mode.
 55. The system of claim 54is further configured to achieve a power factor that is equal to orlarger than 0.9 in the critical conduction mode.
 56. A method forproviding at least an output current to one or more light emittingdiodes, the method comprising: receiving at least a sensed signal, thesensed signal being associated with an inductor current flowing throughan inductor coupled to a switch; processing information associated withthe sensed signal; generating a first current signal, a second currentsignal, and a third current signal based on at least informationassociated with the sensed signal; generating a fourth current signal;processing information associated with the first current signal, thesecond current signal, the third current signal, and the fourth currentsignal; generating a first voltage signal, by at least a capacitor,based on at least information associated with the first current signal,the second current signal, the third current signal, and the fourthcurrent signal; processing information associated with the first voltagesignal and a second voltage signal; generating a multiplication signalbased on at least information associated with the first voltage signaland the second voltage signal; receiving the multiplication signal andthe sensed signal; generating a comparison signal based on at leastinformation associated with the multiplication signal and the sensedsignal; receiving at least the comparison signal; generating amodulation signal based on at least information associated with thecomparison signal; receiving the modulation signal; and outputting adrive signal based on at least information associated with themodulation signal; wherein: the drive signal is associated with at leasta plurality of switching periods, each of the plurality of switchingperiods including at least an on-time period and a demagnetizationperiod; the first current signal represents the inductor current at thebeginning of the on-time period; the second current signal representsthe inductor current at the end of the on-time period; and the thirdcurrent signal represents the inductor current; wherein for each of theplurality of switching periods, the process for processing informationassociated with the first current signal, the second current signal, thethird current signal, and the fourth current signal includes:discharging or charging the capacitor with the first current signal andthe second current signal during only the demagnetization period;discharging or charging the capacitor with the third current signalduring only the on-time period; and charging or discharging thecapacitor with the fourth current signal during the switching period.57. The method of claim 56 wherein over the plurality of switchingperiods, accumulatively, one switching period multiplied by the fourthcurrent signal is equal to a first sum of a first quantity and a secondquantity, the first quantity being equal to the third current signal atthe end of a corresponding on-time period multiplied by half of thecorresponding on-time period, the second quantity being equal to acorresponding demagnetization period multiplied by a second sum of thefirst current signal and the second current signal in magnitude.
 58. Asystem for providing at least an output current to one or more lightemitting diodes, the system comprising: a transconductance amplifierconfigured to receive a sensed signal and also receive a predeterminedvoltage signal through a first switch, the sensed signal beingassociated with an inductor current flowing through an inductor coupledto a second switch, the transconductance amplifier being furtherconfigured to generate a current signal; a capacitor coupled to thetransconductance amplifier and configured to generate a voltage signal;a comparator configured to process information associated with thevoltage signal and a ramping signal and generate a comparison signalbased on at least information associated with the voltage signal and theramping signal; a modulation-signal generator configured to receive atleast the comparison signal and generate a modulation signal; and a gatedriver configured to receive the modulation signal and output a drivesignal to the second switch; wherein: the drive signal is associatedwith at least one or more switching periods, each of the one or moreswitching periods including at least an on-time period for the secondswitch; the transconductance amplifier is further configured to, foreach of the one or more switching periods, receive at least apredetermined voltage signal only during the on-time period; and thecurrent signal is configured to charge or discharge the capacitor. 59.The system of claim 58 wherein: the transconductance amplifier, thecomparator, the modulation-signal generator, and the gate driver arelocated on a chip; and the capacitor is located off the chip.
 60. Thesystem of claim 58 is configured to regulate an output current at apredetermined constant level in a critical conduction mode.
 61. Thesystem of claim 60 is further configured to achieve a power factor thatis equal to or larger than 0.9 in the critical conduction mode.
 62. Amethod for providing at least an output current to one or more lightemitting diodes, the method comprising: receiving at least a sensedsignal, the sensed signal being associated with an inductor currentflowing through an inductor coupled to a switch; processing informationassociated with the sensed signal and a predetermined voltage signal;generating a current signal based on at least information associatedwith the sensed signal and the predetermined voltage signal; processinginformation associated with the current signal; generating a voltagesignal, by at least a capacitor, based on at least informationassociated with the current signal; processing information associatedwith the voltage signal and a ramping signal; generating a comparisonsignal based on at least information associated with the voltage signaland the ramping signal; receiving at least the comparison signal;generating a modulation signal based on at least information associatedwith the comparison signal; receiving the modulation signal; outputtinga drive signal based on at least information associated with themodulation signal; wherein: the drive signal is associated with at leastone or more switching periods, each of the one or more switching periodsincluding at least an on-time period; the process for receiving at leasta sensed signal includes, for each of the one or more switching periods,receiving at least a predetermined voltage signal only during theon-time period; wherein the process for processing informationassociated with the current signal includes charging or discharging thecapacitor with the current signal.
 63. A system for providing at leastan output current to one or more light emitting diodes, the systemcomprising: a transconductance amplifier configured to receive a sensedsignal and also receive a predetermined voltage signal through a firstswitch, the sensed signal being associated with an inductor currentflowing through an inductor coupled to a second switch, thetransconductance amplifier being further configured to generate acurrent signal; a capacitor coupled to the transconductance amplifierand configured to generate a first voltage signal; a multipliercomponent configured to process information associated with the firstvoltage signal and a second voltage signal and generate a multiplicationsignal based on at least information associated with the first voltagesignal and the second voltage signal; a comparator configured to receivethe multiplication signal and the sensed signal and generate acomparison signal based on at least information associated with themultiplication signal and the sensed signal; a modulation-signalgenerator configured to receive at least the comparison signal andgenerate a modulation signal; and a gate driver configured to receivethe modulation signal and output a drive signal to the second switch;wherein: the drive signal is associated with at least one or moreswitching periods, each of the one or more switching periods includingat least an on-time period for the second switch; the transconductanceamplifier is further configured to, for each of the one or moreswitching periods, receive at least a predetermined voltage signalduring only the on-time period; and the current signal is configured tocharge or discharge the capacitor.
 64. The system of claim 63 wherein:the transconductance amplifier, the multiplier component, thecomparator, the modulation-signal generator, and the gate driver arelocated on a chip; and the capacitor is located off the chip.
 65. Thesystem of claim 63 is configured to regulate an output current at apredetermined constant level in a critical conduction mode.
 66. Thesystem of claim 65 is further configured to achieve a power factor thatis equal to or larger than 0.9 in the critical conduction mode.
 67. Amethod for providing at least an output current to one or more lightemitting diodes, the method comprising: receiving at least a sensedsignal, the sensed signal being associated with an inductor currentflowing through an inductor coupled to a switch; processing informationassociated with the sensed signal and a predetermined voltage signal;generating a current signal based on at least information associatedwith the sensed signal and the predetermined voltage signal; processinginformation associated with the current signal; generating a firstvoltage signal, by at least a capacitor, based on at least informationassociated with the current signal; processing information associatedwith the first voltage signal and a second voltage signal; generating amultiplication signal based on at least information associated with thefirst voltage signal and the second voltage signal; receiving themultiplication signal and the sensed signal; generating a comparisonsignal based on at least information associated with the multiplicationsignal and the sensed signal; receiving at least the comparison signal;generating a modulation signal based on at least information associatedwith the comparison signal; receiving the modulation signal; andoutputting a drive signal based on at least information associated withthe modulation signal; wherein: the drive signal is associated with atleast one or more switching periods, each of the one or more switchingperiods including at least an on-time period; the process for receivingat least a sensed signal includes, for each of the one or more switchingperiods, receiving at least a predetermined voltage signal during onlythe on-time period; wherein the process for processing informationassociated with the current signal includes charging or discharging thecapacitor with the current signal. 68.-73. (canceled)